Nao Manual Draft 6n5f1e

NAO Inc. — Property of NAO Inc.

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NAO Inc. Quality Manufacturer of Combustion, Pollution, and Safety Equipment NAO has been deg, manufacturing, and servicing combustion and pollution control equipment since 1912. Our fully engineered systems are installed throughout the world for oil & gas exploration, for oil & gas production, in refineries, in LNG & LPG plants, in loading terminals, and in chemical & petrochemical processing facilities. NAO’s products, systems and services are also widely used in the power generation, pulp & paper, pharmaceutical, and basic metals industries. Our goal is to serve our customers by remaining the worldwide technological leader for industrial burners, thermal incinerators, flares, and other pollution control systems, as well as associated fail-safe and safety equipment.

With the continuity of a three-generation familymanagement team and with manufacturing facilities in Philadelphia, Pennsylvania, Houston, Texas, Milan, Italy, and Tokyo, Japan, we have pursued this primary objective for more than 80 years.

NAO Inc. Regional offices in Asia, Europe, and North America, Representatives in major offices around the world

With the widest range of process flares, including selfcontained, trailer-mounted portable flaring systems, energy-conservation pilots, flame-front and electronicignition systems, subsea ignition systems, flame arrestors, liquid seals, knock-out drums, and the patented, nomoving-parts Fluidic Seal,TM this uncommon organization provides practical, cost-effective solutions to environmental, safety, and energy-control problems throughout the world.


Burners Over 500,000 Installations NAO offers the widest range of industrial burner designs, types, sizes, and fuel-firing options. In some developing nations, burners built by the company before 1920 are still in service because NAO is committed to providing spare parts and service for the company’s “vintage” burners, which, by the way, are low NOx. NAO’s new Low NOx FGITM burners comply with the most stringent worldwide environmental regulations (including California rules 1109 & 1146) by controlling CO and NOx without sacrificing combustion efficiency or flame stability. In addition to burners, NAO designs, manufactures and services a variety of burner packages and accessories. These include: Air Heaters, Burner Control Systems, Flame and Detonation Arrestors, Furnace Accessories, Access Ports & Sightports, Ignitors & Pilots, Incinerators, Inert Gas Generators (a combustor where the products of combustion—carbon dioxide and nitrogen—are used to purge tanks and ships), Process Equipment, Pumping Systems, Specialty Valves, and High-Temperature Castable Burner Tiles.

Flaring Systems Long-Life, Low-Maintenance NAO’s high-performance flaring systems have established the standards for reliability and trouble-free operation for onshore and offshore operations. Our worldwide “standards” are not and cannot be emulated by our competition. For example: The first enclosed ground flare installed in a petrochemical complex in Taiwan achieved only 5% capacity before it failed. NAO was called in to evaluate the defective system, designed and manufactured by another American Company. Subsequently, NAO supplied a total of eight enclosed flares (over $17 million) to several petrochemical complexes that are surrounded by urban development. All of them continue to operate safely, efficiently, quietly, and dependably.

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As part of the flaring systems, NAO designs, manufactures, and services a variety of flare accessories. These include: Energy-Conservation Controls, Flame and Detonation Arrestors, many types of Ignitors & Pilots for NAO and competitor flaring systems. In addition to “flaring” systems, NAO designs, manufactures and services all combustion solution systems including Incinerators (today we use the words afterburner or thermal oxidizer—incinerator is a “dirty word”) and Vapor Control Units.

Flame & Detonation Arrestors Essential Safety Devices There can be no margin for error with a flame arrestor or a detonation arrestor. It must work right the first time, and every time. When a subsonic deflagration or supersonic detonation reaches an arrestor, there is no opportunity to change variables to save your plant or personnel. In 1979, in response to an urgent request for full-scale tests for a nuclear power plant, NAO was asked to design, manufacture and test special detonation arrestors for an explosive mixture of pure hydrogen and oxygen. To accomplish that top-priority project, NAO purchased a 110-acre tract of land near Houston, Texas, which has subsequently been fully equipped and staffed to serve as NAO’s Environmental Research & Service Center. In the past 15 years, extensive full-scale deflagration and detonation tests at the ER&S Center, supplemented by empirical calculations and tests at other NAO facilities, have enabled NAO to design and manufacture the widest range of state-of-the-art deflagration and detonation arrestors, including U. S. Coast Guard accepted units.

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Fully Engineered Pollution Solutions Include Thermal Oxidizers and the World’s Largest Fleet of Emergency Rental Equipment. For efficient control of volatile organic compounds (VOC’s) and other waste gases and liquids, NAO offers a complete line of thermal oxidizers with optional heat recovery sub-systems, liquid & slurry burners, landfill flares, sewage digester flares, sour gas flares, and populated area combustors (enclosed flares). All incorporate state-of-the-art designs for unsured safety, efficiency, and reliability with minimal maintenance. Identified under services, we provide consulation, engineering design, and contractor services. We provide: Emergency Services, such as flare rentals and service (we also rent incinerators and thermal oxidizers in addition to flares), Engineering Services, where someone wants to buy the design package and build it locally, and Field Services, which can include inspection, maintenance and modeling—where we build a model of a burner or a furnace to measure flow rates, heat release, and emissions, and to determine if uniform and proper heat distribution is maintained. We have also developed technical reports on a variety of combustion related topic for customers and for publication. We perform testing on all of our products—burners, flares, pilots, flame arrestors, and detonation arrestors— to demonstrate exactly how they work. With burners, we are actually measuring emission levels of NOx, carbon monoxide, and hydrocarbons so we can provide the customer with accurate information to present to the EPA or their local air control board.

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Manufacturing Excellence Key to Quality As an ISO-9001 manufacturer with a worldwide reputation for dependability that rests on more than 80 years of proven performance, NAO is convinced: Quality keeps customers. NAO always bids to customer specifications. Nothing is “accidently” omitted. Nothing is more frustrating than the loss of an order when a competitor ignores sections of a customer’s specifications; purposely undersizes a burner, flare, or thermal incinerator; omits state-of-theart safety devices; substitutes lighter gage metals; uses simple butt welds instead of full-depth fillet welds; and cuts other corners to submit a low bid only to invoice the customer for “extras” when completing the order.

Keeping Customers Fully Informed As the leader in pioneering innovative, dependable, longterm solutions to the most difficult combustion, safety, and environmental control problems, we have an obligation to keep our customers fully informed. To satisfy this obligation, NAO participates in trade shows and seminars, conducts formal classroom and hands-on training sessions at the “NAO University” near Houston, Texas, and schedules on-site technical presentations throughout the world. For information about trade shows, seminars, flare schools, burner schools, and technical presentations scheduled in locations around the world, send a fax to “NAO Training ” at 215.743.3018. NAO engineers also author dozens of informative reports every year, and reprints are available. For a list of these reprints, send a fax to “NAO Reprint ” at 215.743.3020.

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Principles of Combustion — Property of NAO Inc.

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Principles of Combustion What is Combustion? Combustion, or burning, is a chemical reaction between fuel and oxygen resulting in a release of heat. There are three components to combustion: Fuel, oxygen, and ignition. Oxygen comes from air, with is about 21% oxygen and 78% nitrogen by volume. Most fuels contain carbon, hydrogen, and, sometimes, sulfur. For the purposes of process burners, “fuel” means hydrocarbons—oil or gas. For the purposes of flares and thermal oxidizers, the fuel can be any combustible liquid or vapor. Combustion does not (generally) take place just because fuel and air are brought together; they must be intimately mixed, in the right proportions, and energy must be supplied to start the reaction. The success or failure of combustion equipment in industry depends on the designer’s understanding of combustion processes and how to apply that understanding to solve customer challenges.

Composition of Air* 0% rh 100% rh Oxygen, O2

20.99† 23.20‡

20.62 22.94

Nitrogen, N2

78.03 75.46

76.67 74.63

Argon, Ar

0.94 1.30

0.92 1.29

Water, H20

0.00 0.00

1.75 1.10

Other**

0.04 0.04

0.04 0.04

Combustion Chemistry The chemical elements in common fuel substances are carbon, hydrogen, sulphur, and oxygen. Among these, the true fuel elements are carbon, hydrogen, and sulphur—the presence of oxygen in a fuel molecule always lowers the heat of combustion. For example, methane (CH4) has a heating value of 23,800 Btu/lb (55,350 kJ/kg), while methyl alcohol (CH4O) has a heating value of 10,260 Btu/lb (24,860 kJ/kg). The

Equiv. MW 28.96 28.77 3 Density, lb/ft 0.07632 0.07581 * At 60 °F dry bulb ** CO2, H2, He, Ne, Kr, Xe † % by volume ‡ % by weight


presence of oxygen is an indication that part of the original heat of combustion has been used up. With the exception of carbon, all fuels burn as a gas. Liquid fuels must be vaporized prior to combustion. Hydrocarbons burn with blue and yellow flames. Hydrogen burns extremely rapidly, producing a pale blue flame that is difficult to see (except against a dark background). Carbon burns slowly, producing a bright yellow flame. A hydrocarbon burns yellow due to the dissociation, or cracking, of the hydrocarbon into its carbon and hydrogen constituents followed by separate and rapid burning of carbon. If the same fuel burns with a blue flame, it is due to progressive oxidation without dissociation.

Time – Temperature – Turbulence All combustion equipment is designed around the three “T’s” of combustion: Time, Temperature, and Turbulence. Time is designed into enclosed flares, incinerators, heaters, and furnaces through the space in the combustion chamber. The volume of the chamber is made large enough to retain the gas flow long enough to allow for complete combustion of the volatile gases. For instance, thermal oxidizer chambers are generally designed for flow velocities of 40 ft/second, so the chamber height is 20 feet for ½ second residence time. Temperature is the most important “T” of combustion. Heat is used as the driving force to sustain combustion— it excites molecules and speeds the reaction. If the heating value of a waste gas is high enough, the combustion will sustain itself, allowing for an open flare. In other instances, supplemental heat is supplied through an auxiliary burner, as in a thermal oxidizer, or through an assist gas ring on an open flare. To reduce a customer’s operating expenses, NAO has developed several flares and incinerators that maintain high temperature combustion of low heat value gases without the use of assist gas.

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Turbulence is designed into all of NAO’s combustion equipment with baffles, restrictions, retainers, and patented nozzle designs. Changes in direction and velocity thoroughly mix the combustibles with the air (oxygen) necessary for combustion. Turbulence guarantees effective mixing of fuel and air for complete combustion. If turbulence is not part of the design, separation or stratification of the combustion gases would occur and some of the volatile gases would go through the equipment unburned.

Gas Volume Relationships The volume of any gas that is free to expand increases with temperature and decreases with pressure. When considering gas volume, it is necessary to have in mind the temperature and pressure concerned. When comparing gas volumes, it is always advisable to consider them at the same temperature and pressure. The universally recognized Standard Temperature and Pressure is 60 °F and 1 atmosphere pressure (30 inches Hg). The increase or decrease in the volume of a gas caused by variations in temperature and pressure is easy to calculate by simple proportion. For practical purposes, the volume increases exactly in proportion to the absolute temperature and decreases exactly in proportion to the pressure. This can be summarized by the relation: V1 P0·T1 —— = ——— V0 P1·T0 Another important fact about gases is that under the same conditions of pressure and temperature, equal volumes of all gases contain the same number of molecules. (The number is fantastically large, about 2.7 x 1019 per cubic centimeter.) Once we know this, it follows that the weight of a given volume of any gas will be in proportion to the weights of the molecules it contains. As a comparison, consider a basket containing 1,000 ping-pong balls weighing 1/ 100th of a pound, the total weight is 10 pounds. If the ping-pong balls are removed and replaced with 1,000

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Gas Volumes† MW Hydrogen, H2 Methane, CH4 Water, H20 Nitrogen, N2 Carbon monoxide, CO Oxygen, O2 Carbon dioxide, CO2 Sulphur Dioxide, SO2 Sulphure Trioxide, SO3 †

2 16 18 28 28 32 44 64 80

The weight of these gases in pounds will occupy 380 standard cubic feet, i.e. 2 pounds of H2 at 1 atm and 60 °F.


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golf balls weighing 1/10th of a pound, the total weight increases to 100 pounds. The volume of the basket is relatively unchanged and the number of balls is the same, but the weight increases by a factor of 10, the same ratio as the weights of the individual balls. Knowing this relationship, it can be shown experimentally that the molecular weight (MW) of all gases occupy the same fixed volume at STP (1 atm, 60 °F). For instance, the MW of any gas in pounds will occupy 380 standard cubic feet. If we look at air, for instance, with a molecular weight of 29, we know that 29 pounds of air at STP occupies 380 scf. One pound of air, then, occupies about 13.1 scf (380 ft3/29). In practice, it is rare to get air that is free from moisture—the normal atmosphere contains a significant quantity. Since the total number of molecules of all gases in any volume is always the same, it follows that if there are water molecules present, there must be fewer nitrogen and oxygen molecules. In cases where the climate changes regularly from warm, humid conditions to cold, dry conditions and vise versa,

Reaction

Heat of Combustion† —————————— Gross Net Btu Max. flame per temp.‡

C + ½ O2 → CO C + O2 → CO2 CO + ½ O2 → CO2 H2 + ½ O2 → H20 CH4 + 2 O2 → CO2 + 2 H20 C2H6 + 3½ O2 → 2 CO2 + 3 H20 C3H8 + 5 O2 → 3 CO2 + 4 H20 C4H10iso + 6½ O2 → 4 CO2 + 5 H20 C5H12n + 8 O2 → 5 CO2 + 6 H20 C2H4 + 3 O2 → 2 CO2 + 2 H20 C3H6 + 4½ O2 → 3 CO2 + 3 H20 C4H8iso + 6 O2 → 4 CO2 + 4 H20 C2H2 + 2½ O2 → 2 CO2 + H20 C6H6 + 7½ O2 → 6 CO2 + 3 H20 C6H6liquid + 7½ O2 → 6 CO2 + 3 H20 C7H8liquid + 9 O2 → 7 CO2 + 4 H20 C10H8solid + 12 O2 → 10 CO2 + 4 H20

3,964 14,155 323 325 1,011 1,783 2,572 3,353 3,987 1,606 2,332 3,077 1,498 3,744 17,980 18,300 17,290

†All

3,964 14,155 323 275 910 1,630 2,365 3,093 3,685 1,505 2,181 2,876 1,447 3,593 17,250 17,470 16,690

lb lb ft3 ft3 ft3 ft3 ft3 ft3 ft3 ft3 ft3 ft3 ft3 ft3 lb lb lb

gases are dry at 60 °F and 1 atmosphere. flame temperature when burned with theoretical air.

‡Maximum

3,820 3,960 3,960 3,640 3,710 3,770 3,780 3,720 3,910 3,830 3,810 4,250 3,860 3,840 3,850


this becomes very significant. For example, consider a plant that is set to operate at 10% excess air at 32 °F with nearly zero humidity. One pound of air, then, occupies 12.4 ft3. If the plant requires 1,000 lbs/hr for stoichiometric combustion, the air dampers will be set to 110% air, about 13,600 ft3/hr. Now consider the situation with atmospheric air at 85 °F and saturated with moisture. The volume of one pound of (dry) air is now 13.7 lbs/ft3 and the associated moisture occupies about 0.6 ft3, so the actual volume of air saturated with water at 85 °F is 14.3 ft3. If the burner receives 13,640 ft3 of this air in one hour, the weight of actual (dry) air will be 954 pounds. Instead of 10% excess air, the plant will be operating at 5% deficient air—they are dumping fuel to the atmosphere!

The Primary Refinery Process Composition of Petroleum Oil Crude petroleum is a liquid of varying viscosity. It ranges in color from light brown to black depending on its origin. Crude petroleum is a mixture of three principle classes of hydrocarbons: The paraffins, the naphthenes, and aromatics. Paraffins: These are all hydrocarbons of the formula CnH2n+2. Paraffins can be gases such as methane (CH4) or butane (C4H10), liquids such as hexane (C6H14), or even solids such as Hexadecane (C16H34). The lightest of the paraffin group come from the natural gas associated with the oil. The heavier are distilled from the oil in the refinery. Naphthenes: Napthenes have the general formula CnH2n. Aromatics: Aromatic compounds are all derivatives of benzene, C6H6. In addition to these organic materials, there is also dissolved nitrogen, other compounds of oxygen and sulphur, and come compound of mineral origin such as vanadium.

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Processing Crude Oil The typical refinery process involves fractional distillation of the petroleum oil into its constituent products. These products are often used in secondary processes. To distill the petroleum fractionally, it must first be heated in a fired heater. The types of heaters will be discussed later. In the crude heater, the oil is heated to a temperature of about 660 °F by ing it through tubes under a pressure of 150-200 psig. The oil is pressurized to prevent it from flashing in the heater tubes. Without the high pressure, bubbles of gas would form that can cause the tube to overheat and, consequently, to coke up. The coking can plug the tubes, causing a rupture and a huge fire. Also, on heaters with short-radius turns, bubbles erode the metal as they stream past. While still under pressure, the heated oil is ed to the fractioning column or flash tower. In this column, the hot, pressurized oil flows through an orifice to flash it as a vapor into the low pressure column. The column consists of a large number of trays designed to filter the hot oil vapors. As the hot vapors rise, they cool and condense. The heavy constituents with the highest boiling point condense first, the light constituent—the lighter fractions—will rise to a higher level before they cool sufficiently and condense. When the various oils condense inside the column, they fill up their respective trays until enough of the liquid has condensed to cause it to overflow. These overflows are called sidestreams. In theory, you can remove as many different sidestreams as there are plates, because the oil on each plate has condensed at a slightly different temperature. From a practical point of view, this is not necessary. A number of sidestreams are grouped together in a fraction, the oils which condense over a given temperature range. An example of this is tractor vaporizing oil, all of which distills between 300 °F and 530 °F, with 40% distilling at 390 °F.

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To keep the fractions within specifications, it is important to maintain tight control over the distillation ranges of the sidestreams, and it is necessary to remove the more volatile products that are entrained on trays lower than those on which they would have distilled. This operation is carried out in a sidestream stripper, a vessel that is really only a small, secondary column consisting of a few plates. The sidestream enters the stripper near the top and filters down. Steam is introduced at the base, reducing the vapor pressure and causing the volatile constituents to vaporize. This re-vaporized portion in returned to the column higher up while the sidestream runs out of the base of the stripper.

Secondary Refinery Processes Cracking With the popularity of the internal combustion engine, the demand for light fractions exceeds the limit naturally present in petroleum oil. The process used to produce what does not come naturally is cracking. Cracking is the process of breaking large oil molecules into smaller ones.

Thermal Cracking Thermal cracking offers an inexpensive way to upgrade a major portion of crude oil. In thermal cracking, heavy petroleum distillates are typically subjected to temperatures of 800-930 °F in fired heaters under pressures as high as 400 psig. At this temperature, the long chain paraffinic hydrocarbon molecules break into smaller chains, forming unstable compounds that can be stabilized in pre-determined directions, depending upon the product required. For the gasoline engine, the product is a fuel rich in naphthenes and aromatics; these give good ignition characteristics.

Visbreaking: The visbreaking process is a mild thermal-cracking process that produces low-viscosity

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oils. It is called “visbreaking” because the process breaks the viscosity of a heavy oil. Visbreaking is used to upgrade a heavy, residual fuel oil and make it marketable. Upgrading is often achieved by “cutting” the residual oil with a middle distillate. Visbreaking reduces the consumption of these distillates by about 20%. The basic equipment of soaker visbreaking consists of a fired heater and a fractionating column with a “soaking drum” placed between them. The soaking drum is a reactor in which the cracking takes place. The feedstock is heated to 895 °F and kept at this temperature in the soaker for a pre-determined amount of time before being fractionated. The use of the soaker provides for long residence time, which permits low cracking temperature and saves operational and capital costs. Lower temperatures mean smaller heat exchangers, less coking, and extended tube life.

Coker Cracking: A severe form of cracking converts oil residues into additional yields of naptha for subsequent processing. The residuals are heated to release lighter fractions. If the resulting coke is low in sulphur, the coke can be used in metallurgical processes.

Steam Cracking: Steam cracking is designed to produce raw materials for the petroleum chemical industry. In this case, heat is used to crack a feed of raw gasoline. The feedstock is mixed with steam and quickly heated to a very high temperature. The molecules of gasoline break down or change shape to form light gases (such as ethylene, propylene, butylene, and butadiene) and high-quality gasoline fuel. The cracked products are compressed, refrigerated, and ed through a series of fractionating columns to separate the individual compounds.

Catalytic Cracking In the catalytic cracking process, petroleum oil s the hot catalyst where it is vaporized and reformed into gasoline-rich fractions. The process is sometimes called fluid catalytic cracking. It is “fluid” because the catalyst,

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in the form of a powder, behaves like a fluid when blown with air or oil vapor. In the process, the oil is sprayed into a stream of red-hot catalyst. The catalyst cracks the oil, and the oil fluidizes the catalyst. In doing so, however, coke is deposited on the surface and in the pores of the catalyst so that periodically the catalyst must be regenerated. Regeneration is achieved by blowing air over the catalyst. This causes an exothermic reaction that reheats the catalyst for another with the oil. The regenerator gas has a high carbon monoxide content and is often used as a fuel for a CO-fired furnace. With the efficiency of modern catalysts, less coke is deposited, so regeneration produces less heat and an external heat source must sometimes be used.

Hydrocracking Hydrocracking is a combination of catalytic cracking and hydrogenation. The process involves hydrogen at pressures from 100 to 2,000 psig. Olefinic materials created by cracking are saturated with the hydrogen before they can contribute to coke formation. Hydrocracker units costs more to build and operate than the fluid catalytic cracker, so it is usually used only to supplement the cat cracker process. The hydrocracker will handle heavier fractions better than the cat cracker, and it can be tailored for varying ratios of gas, gasoline, and middle distillate.

Polymerization Polymerization is the reverse of cracking. It is the combination of small molecules to produce larger ones. Light gases produced in the cat cracker are combined to produce heavier gases, like butane, and a further supply of gasoline. Polymerization competes with alkylation for olefinic feedstocks. In polymerization, about 1.4 barrels of olefin feed is necessary to produce 1 barrel of gasoline.

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Alkylation produces gasoline more efficiently, so polymerization of olefins is primarily reserved for the production of petrochemical materials.

Reforming Reforming changes the shape, rather than the size, of hydrocarbon molecules. The need to increase the octane rating of gasoline blends is the major reason for reforming the molecular structure of a petroleum fraction. For example, reformers make high-quality gasoline from the raw gasoline produced by primary distillation. The raw-gas feedstock is ed through a series of furnaces and reactors that use high pressures, special atmospheres, and catalysts to convert straight-chain molecules into aromatic forms. Most feedstocks for reforming are first hydrotreated to remove arsenic, sulfur, and nitrogen compounds that can poison the reforming catalysts. Hydrogen is a by-product of catalytic reforming. Some of this hydrogen is recycled to sustain reactor pressure and to suppress coke formation. The remainder is available for other processes, such as hydrotreating, hydrocracking, isomerization, and the manufacture of petrochemicals.

Isomerization: The process of isomerization reforms normal paraffins into their isomers. The conversion increases octane ratings of the feed significantly. For example, normal pentane with an unleaded octane rating of around 60 can yield its isomer having a rating over 90. Another route to higher octane uses isomerization to convert normal butane into iso-butane needed for alkylation.

Alkylation Alkylation is second to reforming as a means of getting economical octane ratings from processed fractions.

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Alkylation improves the gasoline yield of a refinery by combining gaseous feeds to produce liquids. The process combines an iso-paraffin, usually iso-butane, with olefins such as propylene, butylene, or amylene. The resulting product is a stable gasoline with a high octane rating. The catalysts used for alkylation are sulfuric acid, hydrofluoric acid, and aluminum chloride with hydrochloric acid. Alkylation units have recycle systems to recover these acids for re-use. Alkylation has replaced the polymerization process for the production of gasoline from olefinic feedstocks. In polymerization, 1 barrel of gasoline is produced from 1.4 barrels of olefin feed. When the 1.4 barrels are combined with iso-butane and fed into an alkylation unit, 2.5 barrels of gasoline. The alkylation process also produces a gasoline with a higher octane rating. Polymerization is now used primarily for petrochemical manufacturing. Though, alkylation is used in the production of some petrochemicals. Benzene and ethylene are combined by alkylation to produce ethylbenzene, which is used to form styrene and synthetic rubber.

Hydrotreating Hydrotreaters are used to treat the by-products of olefin manufacture. The by-product liquid are high in aromatic content, but they are contaminated with acetylene and diolefins that polymerize and form sludge. Hydrotreating selectively saturates these molecules without destroying the aromatics. Hydrotreating is used to pre-treat the feedstock of catalytic reformers. Hydrotreatment reduces the nitrogen, sulfur, and other compounds that would otherwise poison the catalysts. For most hydrotreating processes, the pressures range from 100 to 3,000 psig. Temperatures range from 350 °F to 850 °F, though most processing is done in the range 600-800 °F. Hydrogen consumption rates are around 200 scf per barrel of feedstock.

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Solvent Refining Though most separations are made by distillation, solvents can also be used to isolate fractions on the basis of their relative solubility. Solvent refining methods are used primarily to manufacture lube oil fractions and to prepare feedstocks for subsequent processing. Crude oil de-salting is a type of solvent refining. Water is used to dissolve salts and other solid contaminates from the oil before it is subjected to any other refining process. In some cases, other chemicals are added to aid in the de-salting process. In other cases, an electrostatic field is used to improve the separation of the water and solids from the oil.

Gas Treating Gas treating is used to clean up hydrocarbon gases by removing the acidic gases of carbon dioxide, carbonyl sulfide, hydrogen sulfide, and mercaptans. The greatest use of gas treating is in natural gas processing.

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References Cross, Frank L. Handbook on Incineration. Technomic Publishing, Westport, Connecticut: 1972. NAO Book #373

For Additional Reading

For copies of these and other related technical papers, please mail or fax your inquiry to: Literature Department, NAO Inc., 1284 East Sedgley Avenue, Philadelphia PA 19134, Fax 215.743.3020.

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Burners — Property of NAO Inc.

Burners Established in 1912 as a burner manufacturer, NAO has been making burners and combustion systems longer than any of our competition. NAO uses the best and the latest technology to build the best burners on the market. We provide every type of standard burner on the market, and we custom engineer specialty burners for specific client applications. Our burners have been field proven in over 500,000 installations worldwide to have superior turndown and longer life than our strongest competitors. If the customer will provide us with proper specifications, we can supply the best burner for their application. Proper specifications include: Flame Shape, Heat Capacity, Available Fuel, Required Turndown, and Required Draft.

Firing the Burners NAO supplies all types of burners for any fired-fuel application. These burners can usually be fired in any direction, and they can be designed to produced a widerange of flame patterns. The direction which the burner fires will depend on the type of furnace, heater, smelter, or other equipment. Once the direction is known—down fired, up fired, horizontally fired, or angle fired—the acceptable flame shape will be known. The shape of the flame is very important because impingement of the flame on the furnace wall or heatexchanger tubes must be avoided. If the flames impinge upon the tubes, carbon will form inside of the tubes: that will change the heat transfer rate in the tube, actually causing more carbon to build up. The tubes will eventually plug, burn up, and crack, which could lead to a rupture of the tubes and a very large fire, so flame

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impingement is very bad and must be minimized. Therefore, in order to generate a quotation for new or replacement burners, we must obtain some kind of a drawing of the inside of the heater or furnace showing the tubes and walls so our engineers will know what kind of space there is to fire in. We can determine if we need a long or short cylindrical flame or a flat flame. Another important characteristic is burner turndown. Turndown is the ratio of the maximum rate of firing to the minimum rate. NAO burners are known for their excellent turndown, which gives them a wide range of performance that allows customers to fine-tune their fired equipment. When you need good turndown—where the burner is operating at a very low firing rate—the pressures might be only inches of water column, so don’t be too concerned about the minimum pressure. What you want to consider is the maximum pressure available, so that we can analyze this and design a unit with the greatest operating range.

Controlling the Fuel Inspirating Burners An inspirating burner is also known as a pre-mix gas burner (inspirating burners only use gas fuels). Inspirating burners rely on a high-velocity jet of gas to pull in the proper amount air so you have a stoichiometric gas and air mixture. Inspirating burners are unique among gas burners in that the gas and air mix before combustion starts to take place. NAO makes many types of pre-mix burners. One of NAO’s original inspirating burners is the Rams Horn Inspirating Gas Burner. The Rams Horn is a burner that splits into two burner heads. Normally, these are mounted underneath the furnace on a track that allows them to slide in and out for easy removal and maintenance. They fire up from the floor of the heater, and usually at a slight angle. The flame bounces off a wall, from which the heat radiates.


Raw Gas Burners Raw Gas Burners are also known as Nozzle Mix Gas Burners. With the Raw Gas Burners, the gas and combustion air do not mix until the gas leaves the ports of the burner. The key to stable combustion in a Raw Gas Burner is turbulence. NAO burners use the patented Jet Mix burner tip to deliver a turbulent vortex of raw gas into the combustion air stream. The gas and air mix very well for complete and stable combustion of the burner flame.

Controlling the Air Natural Draft Burners A natural draft burner works due to buoyancy of the hot gases in the stack. The fact that you have hot air and it has lower density it will tend to float up, creating a negative pressure in the furnace. Natural draft is a function of the change in density of the expanding gas and the height of the flue stack.

Induced Draft Burners Induced draft is very similar to natural draft. Natural draft is where you have a negative pressure pulling the air through the burner. Induced draft is created by a fan in the flue stack. It is usually a high temperature fan because the products of combustion in the stack are very hot.

Forced Draft Burners Forced draft burners have a fan pushing air through them, so it is under a positive pressure. By pushing more air through the burner, you can push more fuel through it and increase the its heat release. Forced Draft Burners can also come with natural draft back-up. This is usually important when a heater or furnace must remain in operation if the air blower that supplies the forced draft fails. There is a or a trap door on the air

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plenum, so that if the forced draft fan fails the door will automatically open. These burners usually have some kind of electronic catch or a pneumatic cylinder so when the fan fails the door pops open. Air is sucked in by the chimney effect of the furnace. At this point, heat release may drop to 50% of the normal forced-draft rate.

High Intensity Burners “High intensity” means that the combustion is very intense. You have a very short, very well knit flame. These are a swirling type of injection burner. They are also very stable and are used mostly for boilers, dryers, kilns, and other process furnaces. High intensity burners were developed to improve efficiencies of cabin-fired heaters and furnaces. Most burner flames are typically about one-million Btu’s per foot, so if you have a 10-million-Btu burner, you have roughly a 10 foot flame. When you have a high intensity burner, 10million Btu’s, it would only be a two-foot long flame. Or, in other words, about 5-million Btu’s per foot. Now this is important for certain process units if it is a very-small, verytight type of unit. Then you can obtain a lot of heat release in a very small space. In the center of some NAO burners, in place of the oil gun, is a gas burner. The holes in this type of gas burner are drilled in such a fashion that, as the gas comes out, it swirls in a vortex. This way you can get very good flame stability and also a very short, intense, and clear blue flame. NAO has a patent on this type of burner. NAO High Intensity Burners perform very well, but at a price. The hotter flame of a high intensity burner generates a lot of NOx. To meet new requirements, we have incorporated the latest technology into NAO burners to satisfy the most stringent NOx emission requirements.


Controlling Flame Direction Vertically Fired Burners Vertical fired usually means the burner flame is directed vertically upward or downward. A vertically-fired burner can be either a radiant wall burner or a cylindrical flame burner. Air heaters and furnaces generally use vertically upfired burners. Down-fired burners are very common in Ammonia Reformers where ammonia or fertilizer is made. The burners are mounted in the roof of the furnace and all the flames are downward.

Horizontally Fired Burners Horizontally Fired Burners are mounted horizontally. It is mounted in the wall of a heater and fire out along the radiant floor to heat it up or they might fire above the floor so that it is just a cylindrical flame. This information will be specified on the drawing or sketch provided by the customer.

Angle Fired Burners Angle firing means the burner is at any angle between downfired and up-fired. Angle fired burners are often directed at a furnace floor or a radiant wall, like the NAO Rams Horn Burner (an inspirating burner).

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Controlling Flame Shape Cylindrical Flame Burners

Typical Flame Length for Cylindrical Burners Natural Draft

1 foot —–———— 1 MM Btu

Forced Draft

1 foot —–———— 2 MM Btu

High Intensity

1 foot —–———— 10 MM Btu

Most conventional burners have a cylindrical flame. A cylindrical flame is either a pencil flame where the cylinder is long and thin, or it is (on a high-intensity burner) a short and wide flame. To reduce pumping costs, the cylindrical burners are usually designed for very low pressures, like the NAO Low Pressure Cylindrical Gas Burner designed for fuel pressures of 2 to 5 psig.

Flat Flame Burners

Typical Flame Length for Flat Flame Burners Natural Draft

1 foot —–———— 1¼ MM Btu

Forced Draft

Not standard

High Intensity

Not standard

Flat flames look like a Japanese fan. Broad side, the flame has a “V” shape; turn it 90° and it is wide but not very high. The flat flame can either be fired up along a wall, or horizontally along a floor. Flat Flame Burners are usually put in heaters or furnaces that are long and thin and that require a wide flame with a very uniform heat distribution. As always, it is very important to that you do not want to have the flames from the burner to impinge upon the tubes inside the heater. Flat Flame Burners are often inspirating gas burners, but the term “flat flame” can also apply to oil fired burners. On combination oil & gas burners, the Hexad gas tips are usually drilled to produce a flat flame.

Spider Burners A Spider Burner, for example, is a burner that looks very much like an old fashioned turnstile or a star. There is a hub with eight arms radiating from it, like your gas stove at home. This produces a very short, intense blue flame.


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Radiant Wall Burners A radiant wall burner is usually a pre-mixed or inspirating burner that functions by firing into or across against a floor or wall. There are three types of radiant wall burners: Wall-mounted burners, floor-mounted burners, and side-mounted burners. Wall-mounted burners fire back against refractory-lined walls. Wall-mounted burners have a flame that looks like a flower or a daisy that is pressed against the wall. Floormounted burners fire up along refractory-lined walls. Sidemounted burners are wall-mounted, up-fired burners that are up-fired out of and along refractory-lined walls. The refractory lining absorbs and radiates heat throughout the burner chamber. Because the chamber is heated by radiation from the wall, slight variations in burner heat output are eliminated and heating is very uniform.

Radiant Wall Burners Wall-Mounted

Floor-Mounted

Side-Mounted

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Burner Fuels NAO can supply a burner for almost any fuel. It is not uncommon for NAO to supply a burner that uses three different fuels. In the gas category, almost anything that is combustible, including hydrogen and low-heat-value gases such as carbon monoxide (CO), or other combustible gases diluted with inert carbon dioxide (CO2), nitrogen, or water vapor. Typically, though, NAO burners use methane (natural gas), propane and refinery off-gases. Refinery gases are a little rough, because you don’t know exactly what those waste gases include. Natural gas is a common constituent, but other gases, including hydrogen can be present. These off-gases come from pressure relief valves that dump into the header system. One moment it is a very heavy fuel with a lot of butane in it, the next moment may bring high hydrogen content. The sudden change in fuel will affect the flame shape, and with pre-mix burners the sudden high hydrogen content could cause flashback. In the past, the refineries vented many of these gases, but with concern about smog and the greenhouse effect, venting of volatile organic compounds (VOCs) isn’t acceptable these days. These VOC’s must be collected and incinerated in an afterburner or thermal oxidizer, or put into a boiler or furnace to produce heat. In this way, refineries now recover some of the money they used to “throw away.”

Oil Fired Burners Under the category of oils, there are various liquid fuels and alcohols. In the pharmaceutical industry, they use alcohols to manufacture pills and medicines. The contaminated alcohols must then be burned off, so this liquid waste could be just about anything. Sometimes the liquid waste burns to produce secondary pollutants like chlorine gas or sulphur dioxide. In these instances, a scrubbing system is required to get rid of the chlorine or the sulphur dioxide. Oil Guns are used for firing Naptha and refined & crude oils. Naptha is similar to lighter fluid. Number 2 Oil is diesel fuel. Number 5 Oil is a heavy oil, and Number 6 is the heaviest standard grade of oil. Usually, #5 and #6 oil are used in heating very large buildings. Bunker C is a very


heavy oil. It is nearly the lowest grade and it is used mostly in refineries for process heat, otherwise, it would be wasted. Naptha can be a safety hazard if the burners are not designed properly or if the s are careless. Since it is a very light fluid, if it gets only little bit hot, it will flash and turn to gas; but it doesn’t burn well as a gas. NAO’s special gun for Naptha burners utilize two separate pipes to keep the Naptha cool to prevent flash-over. NAO oil burners can also fire an oil-water emulsion. This is where you have water mixed in with the oil—usually in the range of 10 to 20%. When you get more that 30% water, it is not going to burn well and the flame will be unstable. Such an emulsion may be used if you have very dirty oil. It makes the dirty oil burn cleaner, with less particulate and less NOx. Besides refined oils, our units also burn various tars and crude oil. When selecting burners to fire these heavy “fluids,” you must know their viscosity. You can think of viscosity as the opposite of fluidity. If the viscosity is too high, fluidity is low, and the tar or oil must be heated before it flows through the burner. Tars are hard to burn because they have to be heated to a very high temperature before they flow through the pipes and to burn. Crude oil is usually relatively easy because it is light weight, though this can be a safety problems because crude can contain a lot of light gases that flash readily; therefore, crude oil must remain under pressure until it is fired at the burners. Oil guns can also be used to incinerate solids, coal dust, and coal particles, either in a solvent or in an oil. Solvent Refined Coal (SFC) is a way of having coal in a liquid form, so it can be pumped for use in burners. The coal is crushed to a very fine powder and mixed in oil. This type of slurry was fairly common in the 1970’s during the energy crises. NAO has not handled many jobs like this recently, but we still maintain the capability.

Oil Atomizers To make oil burn efficiently, the liquid must be broken up (atomized) into very small droplets that can vaporize quickly. The smaller the droplet, the greater the ratio of surface area to volume; so, more heat is absorbed per unit volume in a

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given amount of time, and the oil vaporizes more quickly. NAO makes different types of oil atomizers: Steam, Air, Gas, Mechanical, and Dual-Stage (mechanical/steam or gas/ steam). Steam atomization is the most common oil atomizing medium. When we use the word steam, that you can substitute compressed air, high-pressure natural gas (around 100 psig minimum), or any other high pressure gas—even nitrogen and carbon dioxide. Though, normally you would not want to use an inert gas because they dilute combustion. In some cases, where you don’t need much turndown, you can use pure mechanical atomization. However, this is rare, and this is where the dual stage comes into play. Mechanical atomization works good at high rates, but at lower turndowns it starts to fall off, so steam atomization will complete the job. This is dual-stage atomization. Dual-stage atomization using inert gases and steam is often used on ships. On a ship there is no start-up steam to start a boiler burner with steam atomization. Ships do have bottled CO2, however, that can atomize oil to get some heat into the boiler. When the boiler is operating and making steam, the atomizing medium is switched from CO2 to steam. In special cases like these, you may be able to employ process gases, such as with the Low Pressure Air Atomizer. This is actually uses a mechanical atomizer for the oil at first, then air hits the oil spray and breaks it up further.

Oil Gun Safety If you look at the bottom of an oil burner, at the very lowest point, you see the part of the oil gun known as detaching gear—something similar to a horseshoe that fits around the burner gun. A handle allows you to unscrew the gun and pull it out for cleaning. If an operator is careless, the oil gun may be removed while it is under pressure. If the pressurized line contains crude oil with dissolved light gases, these can flash suddenly, ignite from surrounding burners, and cause a tremendous fire. To protect personnel against such accidents, NAO can supply oil guns with safety interlocks.


Oil Guns often come with Safety Interlocks when used with very light fuels—alcohol, naptha, or waste gasoline—you have to be very careful. Any leaks could flash and cause a major fire. Safety interlocks prevent the operator from removing a gun until everything is shut off and all valves are closed. The interlocks are two valves that, when closed, shield the oil gun. Closing the valves moves the shields, allowing for the removal of the oil gun for service. These interlocks prevent an unsuspecting plant operator from opening a pressurized line of volatile products and causing a major fire.

Gas Fired Burners Low Pressure Gas Burners Low Pressure Gas Burners are generally can be Multi-Jet Burners or Multi-Tip Burners that rely on low pressure gas (less than 2 psig).

Hexad Gas Burners Generally surrounding the Oil Guns or Low Pressure Gas Burners are four to eight Gas Burners. These are NAO Hexad Gas Burners. The Hexad is designed for pressures of about 10 psig as a minimum and with pressures to 50 psig at the maximum rate. Hexads are mounted on two semi-circular manifolds that surround the main oil and gas burner. The reason for this design is so you can remove these burners for easy maintenance or cleaning. Sometimes refineries have very dirty gases with a lot of condensate (liquids like propane or butane) that cause problems because they tend to flash and coke inside the burner standpipes, eventually clogging the burner. To remove the Hexad Burners, you normally increase flow to the oil burner or the low pressure gas burner so the unit is still operating, then you remove the Hexad manifold with the standpipes and tips to perform the required maintenance. Many times the oil gun will also require maintenance. Oil is very dirty stuff, and it is very likely to drip if you do not have the atomization properly adjusted. So, the total unit is designed either to fire the oil cylindrical gas burner (the Low Pressure Burner) while

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working on the Hexad or to fire the Hexad while working on the oil or cylindrical-gas burner. You can always keep an NAO burner in operation and firing while doing maintenance work. NAO manufactures different types of gas burners, oil burners and combination burners. The burner can be dual gas, such as waste gas and fuel gas; it can be tri-fuel, such as gas, waste gas and oil. One very important design feature of burners is low excess air, which affects the burner efficiency. If you allow a lot of extra air into the burner, it is going to waste a lot of energy because it has to heat up this extra air. The air is going along for a “free” ride. The way you control the amount of excess air is with very tight air control. This means that the air dampers must be able to shut tightly and the furnace walls and floor must be sealed. If an NAO burner is out of service because it needs cleaning or maintenance, you can close the damper off fully so no extra air will leak into the heater and degrade your efficiency.


Burner Controls NAO supplies packaged control systems with infrared (IR) and ultraviolet (UV) flame scanners to control the pilot gas, the fuel oil, and the fuel gas of our burners. We also supply a number of air damper designs, manual and automatic, to regulate the amount of air going into the burner. With over 80 years of burner design experience, we can provide a complete burner package at a great price to satisfy any customer. These package systems can range anywhere from $5,000 to $150,000. NAO provided a large, Air Heater package to Fina in Houston for $400,000. NAO also supplies various types of oil and steam indicating valves to regulate steam and oil for various oil burners. They actually have a dial right around the top so you can see the fuel setting at the burner.

Packaged Systems Package burner systems are burners with the blower, the wind box (the duct work where the air enters the burner), and all of the controls necessary for efficient operation. A common packaged system is the Oil Patch Burner. This burner is used in heater treaters in oil field production. For more information, see the applications section.

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Burner Pilots NAO makes several types of burner pilots. The most simple is an inspirating pilot with manual ignition. We use these on natural draft burners. The pilot gas is injected into a bell mouth inspirater to draw in combustion air. Manual ignition saves money because operators can use one handheld ignitor to light many burners.

Burner Pilot Ignitors NAO has several Hand-Held Ignitors. One is actually a pilot attached to a long rubber hose with a pressure regulator from a propane bottle. It is used to light off all the burner pilots within reach of the hose. Another Hand-Held Ignitor is the NAO Portable Ignitor. It has a propane bottle, a sparker, and a battery. We also have a newer version—the NAO Portable Burner Ignitor, NPBI—that does not need a battery. These are costeffective and safe alternatives to the “traditional” method of using a burning rag to light pilots. NAO also makes a Spark-Ignited Burner Pilot. It has a spark generator near the inspirater with a long electrode that extends to the nozzle where it produces a spark. NAO has a High Energy Electronic Ignitor, used on air heaters or reactors. Often we sell them to customers for chemical reactors. It generates sparks to ignite the burner. This is a retractable ignitor, so once we prove the flame, either with a UV scanner or some other means, then it pulls out to prevent burn up.

Burner Pilot Controls Burner pilot controls are used to sense if the pilot is operating. When the pilot is burning, the controls are satisfied, if not, the controls may try to re-light the pilots or lockout the main fuel and sound an alarm. The response of the controls will depend on the design requirements.


Two common methods of sensing the pilot flame are flame ionization rods and ultraviolet (UV) scanners. With the ionization rod, the flame hits the rod, and the rod senses that the pilot is running. The flame rod es a very small current, just a thousandth of an amp, but enough to sense ions formed in the pilot flame. The UV scanner looks for UV rays generated in the pilot flame. These are very good flame sensors because they can focus on the pilot and instantly detect if the flame goes out. Before the development of UV sensors, infrared (IR) detectors were commonly used to monitor pilot flames in burners. (IR detectors are still commonly used to detect pilot flames on flares.) IR sensors do not work well on burner furnaces, however, because, in the heat of the furnace, the IR sensors cannot detect the difference between the heat of the pilot and the heat of the furnace floor and walls. UV sensors offer the advantage of detecting flame, not just heat.

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Burner Efficiency Air Pre-Heat Combustion System Check List for energy-cost reduction √ Multi-fuel capability

An air pre-heating system reclaims heat from the flue gas and adds that heat to the air required for combustion. Air pre-heaters are often used on forced-draft systems to increase burner efficiency.

√ Unconventional fuels √ Combustion efficiency √ Low excess air √ High swirl √ Heat recovery √ Minimize losses in walls and stack √ Controls for optimized operation

With standard oil and gas burners, the efficiency of the overall performance of the burner system will increase about 2% for every 100 °F increase in air temperature. Pre-heating air creates two potential problems. First, heating the combustion air raises the temperature of the combustion products in the heater, which increases the formation of NOx. There is a trade-off between efficiency and pollution control. Second, pre-heating the combustion air with the stack gas can reduce the gas temperature below the dew point of the sulfur compounds in the products of combustion. If this occurs, H2SOx can forms and collect on the walls of the stack, accelerating corrosion of the metal.


Burner Noise Burners tend to create noise—almost like a rocket taking off. This is a big concern, particularly since the early 1980’s when OSHA required that we have various means to quite down the burners. We use either individual noise shrouds or plenums. A plenum is a large box you put around the burners. This will be illustrated in some of the later photos. We have Acoustically Shrouded versions of all NAO burners. Basically, the shroud is a metal box with an acoustical inner lining to absorb combustion noise and the high-frequency noise of steam and gas injection. The acoustical plenums can serve additional purposes. They are insulated, so they reduce heat loss through the bottom of the burner. Sometimes, the plenums are designed to circulate water and thermal fluids to preheat air to improve burner efficiency. However, this usually raises NOx levels, so you have to balance air pollution versus efficiency.

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Low NOx Burner Technology Since the introduction of high intensity burners in the 1960’s, NAO has developed the technology to reduce the formation of NOx in the combustion flame. We have incorporated the latest NOx technology into NAO burners to satisfy the most stringent emission requirements. Interestingly, NAO’s original burner designs like the Rams Horn burners have proven to be some of the best Low NOx burners on the market. NOx formation is a function of the temperature of the flame. Cool flames do not produce NOx, but cool flames are not as efficient as the high-intensity flame of modern burners. As a compromise, NAO has developed staged-combustion burners and burners that re-circulate the flue gas to reduce NOx while maintaining hot flames. Before exploring the design methods to limit NOx, we can explore the factors that either cause, or increase, NOx production. NOx includes all oxides of nitrogen, this can be NO, NO2, or NO3. The factors mentioned are not necessarily in order of importance.

Factors Leading to NOx Formation 1. 2. 3. 4. 5. 6. 7. 8.

Flame Temperature Furnace Temperature Residence Time at High Temperature Bonded N2 in the fuel. Hydrogen in the fuel High Molecular Weight (MW) of fuel Un-saturated fuel Temperature of combustion air

Oxidation of part of the free nitrogen in the combustion air is the source of NOx, except in Item 4. Chemically bonded nitrogen oxidizes to NOx in higher proportions than free N2 in air. Hydrogen in the fuel (Item 5) increases NOx for two reasons. First, the flame temperature is higher, and second, NOx formation increases because the quantity of flue gas


per heat generated is lower. Hydrogen releases a tremendous amount of heat per unit mass (51,600 Btu/lb) compared to other gaseous hydrocarbons (~21,000 Btu/lb) It is obvious that among items 1-8, some factors are not easily changed. The one pertinent, changeable factor is flame temperature. For a given fuel, it is reduced by a number of methods, which are: A. Staging Air, in which the initial (primary) combustion is starved for air (approximately 75% of theoretical), with second stage air making up the completed combustion. High-intensity burners with very hot flames generate fairly high NOx levels. By using staged air, we can reduce these NOx levels. NAO burners have a series of slots around the outside of the burner to provide staged air (also known as secondary air). The slots surround a large main opening where the main flame emerges. B. Staging Fuel, in which the primary stage fuel (approximately 60% of total) is given all the combustion air needed (100% of total), reducing its flame temperature, with the remaining fuel injected at a higher level, maintaining the lower flame temperature. This method is superior by some 20 parts-per-million-by-volume (ppmv) to Staged Air. This is a good time to insert the observation that, among standard unstaged burners, the pre-mix or bi-mix types are superior by several parts-permillion to raw gas types; but both are inferior to staged fuel burners. It may also be noted that stringing out the combustion process results in longer, lazier flames than industry has grown to demand. C. Injection of Steam into the combustion air. D. Injection of Inerts (CO2, H2O, but not N2) into the fuel stream. E. Recirculated Flue Gas (20-30%) into the combustion air. This is the ultimate procedure, producing NOx in the 20-ppmv range, but it is far

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3-20 Technologies NOx Control


Technique

Descriptions

Advantages

Low Excess Air

Reduces available oxygen

Simple modification Low NOx reduction High CO emissions; All fuels by closing air potential Flame length; dampers Flame stability

1-15%

Off-Stoichiometric Combustion a. Burners out of service b. Overfire Air c. Air lances

Staged combustion creates fuel-rich or fuel-lean zones reducing flame temperatures

Low operating cost; a. Typically requires Flame length; No capital cost for high air flow to Forced-draft fan burners out of control CO capacity; Burner service emissions header pressure b. Relatively high capital cost for additional blowers c. Moderate capital cost

All fuels; Multiple-burner devices

30-60%

Low-NOx Burners

Provides internal Low operating cost; staged combustion Compatible with and/or recirculation, FGR as a thus reducing peak combination flame temperatures technology to maximize NOx reduction

Forced-draft fan capacity; Flame length; Design compatibility; Flame stability at high turndown

All fuels

30-50%

Flue Gas Recirculation (FGR)

As much as 20-30% High NOx reduction Moderate to high of the flue gas is for natural gas and capital and mixed with low-nitrogen fuels operating costs; combustion air, thus Will affect heat decreasing peak transfer and system flame temperatures pressures

Forced-draft fan capacity; Furnace pressure; Burner pressure drop; Flame stability at high turndown

Gas fuels and low-nitrogen fuels

40-80%

Water/Steam Injection

Injection of steam or water at the burner to lower peak flame temperature

Moderate capital Efficiency penalty Flame stability; Gas fuels and cost; NOx reduction with additional Efficiency penalty low-nitrogen similar to FGR water vapor loss fuels and fan power requirements for increased mass flow

40-70%

Reduced Air Preheat

Reducing air preheat High NOx reduction Significant Forced-draft fan Gas fuels and reduces flame potential efficiency loss (1% capacity; Efficiency low-nitrogen temperature drop per 40 °F penalty fuels reduction in air preheat)

25-65%

Disadvantages

Moderate to high capital cost; Not applicable to all burners and fuels

Impacts to Consider

Applicability

NOx Reduction

Selective Catalytic Catalyst located in High NOx removal Very high capital Space requirements; Gas fuels and 70-90% Reduction flue gas stream cost; High Ammonia slip; low-sulfur fuels (usually upstream of operating cost; hazardous-waste (liquid and solid) air heater) Extensive ductwork disposal promotes reaction required; Increased of ammonia (NH3) pressure drop may with NOx to require inducedproduce H20 and N2 draft fan or larger forced-draft fan; Reduced efficiency; Ammonia sulfate removal equipment required; Water treatment of air heater wash required Selective Noncatalytic Reduction)–Urea Injection

Injection of urea into furnace to react with NOx to form nitrogen and water

Selective Noncatalytic Reduction– Ammonia Injection

Injection of Low operating cost; ammonia into Moderate NOx furnace to react removal with NOx to form nitrogen and water

Low capital cost; Simple system; Moderate NOx removal; Non-toxic chemical

Temperature dependent; Design must consider operating conditions; NOx reduction may decrease at low loads

Furnace geometry All fuels and residence time; Temperature profile

25-50%

Moderate to high capital cost; Ammonia handling, storage, vaporization, and injection equipment required

Furnace geometry All fuels and residence time; Temperature profile

25-50%


and away the most expensive, requiring a stack exit nozzle, piping to an induced draft fan by way of a heat exchanger to reduce temperature to a level tolerated by the fan. At the same time, a forced draft fan brings new combustion air in at a pressure equal to the inducer’s discharge pressure. Recirculation will add hundreds of thousand dollars to a large heater installation. For purposes of developing low-NOx burners in the reasonable-price category, NAO has concentrated on burner design using the staged-fuel format. In early designs, burners were built in round and rectangular shapes, with pre-mix and raw gas first stages, and raw gas second stages, in all proportions of distribution ranging from 90% primary and 10% secondary to 10% primary and 90% secondary. Two salient observations came to light: Lower Btu burners were superior to higher, and rectangular burners were superior to round. With the exception of one round, floor-mounted, verticallyfired burner with recirculating features resulting in NOx emissions around 35 ppmv, all the tested burners are capable of being fired vertically up or down, or horizontally with equal results.

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Burner Applications Oil Patch Burners Oil Patch Burners are used in oil production fields to heat crude so its pumps more easily. Oil Patch Burners are usually very simple. They come with a jet mix burner, pilot, damper and flame arrestor. At the bottom of the housing—the for the burner--you can see a flame arrestor sandwiched between two square flanges. This flame arrestor grid prevents flashbacks and explosions if there happens to be any gas in the air that gets drawn into the burner.

Fuel Pumping Station We have built a number of packaged burner units to run Fuel Pumping Stations. Tars and other very heavy oils must be heated to be pumped. Sometimes you must heat them to 300 or 400 °F before pumping is possible.

Submerged Combustion Units Submerged Combustion Units are burners that fire down into a water seal or pot of water. Submerged Combustion Units are used to evaporate or heat water, particularly when large quantities of hot water are required. The submerged burner is very efficient because all the heat of combustion goes into the water stream. Machine shops use these burners to clean water-base cutting oils. The submerged burner is a way to evaporate most of the water and reduce the cutting oil to a very low volume so it can then be landfilled—with volume reductions of 90 to 95%, there are substantial savings in disposal expense.

Inert Gas & Nitrogen Generators Inert Gas Generators are usually fired by diesel, natural gas, or propane, to produce water, nitrogen and carbon dioxide. Most of the time, a dryer is used to remove the water. The desired product is nitrogen and carbon dioxide. The Inert


Gas Generator is a way of providing inert gas for tanks and vessels. Another recent focus of NAO activity is nitrogen generators. These use carbon beds or membrane-filter technology to extract nitrogen from compressed-air or forced-draft feeds. We hope to see these used on flare stacks to purge the line and prevent air ingress. Customers now rely on natural gas or refinery gas to purge their lines, but this can be expensive, and it is not an environmentally friendly procedure. With NAO’s next-generation, mini Inert Gas Generator, customers will be able to provide an inert purge gas to their flares at a very low operating cost.

Duct Heater Duct heaters are a type of air heater. They are used on turbines that are used for standby power. In cities where the power plants are not large enough to handle the peak power requirements, for example, gas-fired turbine generators cover peak electric loads. These turbine generators tend to be very inefficient, so they use a duct burner on the turbine’s exhaust, which has a large air volume at around 500 °F. By installing an NAO duct burner, the exhaust is heated and pushed through a boiler to recover the heat as steam to make more electricity.

Fire Simulation Systems NAO has developed a number of packaged, real-worldconflagration test systems for firefighters to use for skills training. NAO’s simulation systems incorporate unique burner heads, reliable pilots, high-energy ignitors, fail-safe valves, fire-proof wiring, and optional fire-snuffing systems to deliver safe simulations of conflagration disasters at professional firefighter schools.

Specialty Burners NAO custom engineers many specialty burners. We once made burners for the incineration of disposable paper clothes that people wear at a nuclear facility. When they

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come out, the paper clothes are burned and the radioactive ash and dust are accumulated and stored. We are also currently developing a burner system for the incineration of High Explosive Dust, a contaminant generated during the production (and de-commissioning) of nuclear warheads. Our burners will be used to “sterilize” equipment as it is removed from service and before it is landfilled.


Common Problems with Burners No pilot spark Shorted electrode gap: Moisture, corrosion, or other particulate from the pilot gas stream can collect between the spark-ignition electrode. Improper grounding: If the electrode is not grounded, there is no potential difference between the electrode and the pilot wall that causes an electric arc to ignite the pilot gas. Ignition transformer: The ignition transformer may not be receiving power, or the transformer is burned up and not allowing for age of electric current.

No pilot flame Blocked jet: The pilot jet orifice is blocked due to particulate from the gas or from corrosion. If the problem is persistent, consider installing pilot gas filters. Low (or high) gas pressure: Low gas pressure creates a gas mixture with too much air for ignition. High gas pressure creates a mixture with too much gas for ignition. High pilot-air flow: If the air inspirater is open too far, the pilot jet inspirates too much air for the pilot to light. High combustion air flow: Burner combustion air affects the pilot. On forced-draft and induced-draft units, the air blowers should be at their low-fire settings to avoid diluting the pilot gas mixture. UV Scanner detects spark: If the scanner detects the pilot spark, it thinks the pilot is lit and it stops the ignition sequence. The UV scanner can be aimed at the top of the pilot nozzle rather than directly into the nozzle.

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Small pilot flame Partially blocked jet: The pilot jet orifice is blocked due to particulate from the gas or from corrosion. If the problem is persistent, consider installing pilot gas filters. Plugged filter: A plugged pilot gas filter will allow for correct pressure settings but will prevent gas flow. Low gas pressure: Low pressure means low gas flow. Check for obstructions in the gas line/header and for partially closed valves. High pilot-air flow: Allowing the pilot to inspirate too much air can cause a small (generally unstable) flame. High combustion air flow: High combustion air flow will push the pilot flame into the pilot nozzle.

Unstable pilot Wet gas: Water condensate in the pilot gas absorbs heat energy from the pilot flame and leads to instability. Low (high) gas pressure: Low gas pressure allows the flame to be diluted with too much pilot and burner combustion air. High gas pressure can cause the flame to lift-off from the pilot nozzle. Too much air: Improper pilot air adjustment allows too much air in the pilot. This should be evident by an intense blue pilot flame. Not enough air: Improper pilot air adjustment allows too little air in the pilot. This should be evident by a lazy yellow flame Partially blocked jet: The pilot jet orifice is blocked due to particulate from the gas or from corrosion. If the problem is persistent, consider installing pilot gas filters. High chamber draft: High combustion air flow can blow out the pilots.


Gas burner will not light Too much air: Too much air dilutes the gas beyond its upper explosive limit. Check damper and fan settings. Too little fuel: Not enough fuel in the air/gas mixture on forced-draft and induced-draft units can be caused by lowgas pressure or by obstructions in the gas header. Low fuel pressure: Low pressure leads to low gas flow. Plugged strainers: Plugged gas strainers block flow even when supply pressure is adequate. Small pilot flame: Short pilot flames can miss the air/gas mixture of the burner. Interlocks improperly set: Interlocking valves not fully open restrict flow to the burner. Strainers in wrong position:

Oil burner will not light Poor atomization: Oil must be properly atomized for stable combustion. Causes of poor atomization are listed in the next section. Oil and steam connections reversed: Crossing the connections always causes poor atomization. Low combustion air: Improper air settings or restrictions in the air header lead to a mixture too rich in oil too burn. Plugged strainers: Plugged strainers block flow. Small pilot flame: Short pilot flames can miss the air/oil mixture of the burner. Interlocks improperly set: Improper setting of interlocking purge valves will allow steam or inert gas in the main fuel line. Gun positioned improperly: Positioning the oil gun incorrectly may place it out of range of the pilot.

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Poor atomization Low oil temperature: Heavy oils—#5, #6, Bunker C— and tars must be pre-heated before they flow properly through pipes and before they can be atomized properly. Low steam flow: Low steam (or compressed air or highpressure gas) flow can be caused by low pressure or by obstructions in the header piping. Low oil pressure: Low oil pressure can be caused by partially blocked valves or plugged strainers. Low steam pressure: High pressure steam (or compressed air or gas) provides the energy to atomize the oil. If pressure falls off, its atomizing effectiveness is reduced. Oil and steam connections reversed: Crossing the connections always causes poor atomization.

Distorted burner flames Incorrect burner positioning: The refractory tiles of burners stabilize the burner flames. If the burner is incorrectly positioned, it will be close to some tiles and far from others. The tiles close to the burners will absorb and radiate a dis-proportionate amount heat, distorting the burner flame. Tips turned wrong direction: Burners are designed to fire symmetrically. Check the burner design for the proper angle for tip alignment. Some burners have the tips firing at an angle to cause a swirling and turbulent cylindrical flame. Incorrect burner tips: Burner tips are drilled for specific gas compositions and pressures. Mis-matching replacement tips with burners will cause firing problems. Incorrect tip drilling: Burner tips are drilled for specific gas compositions and pressures. Corrosion of tips: Tips can be plugged due to corrosion of the heading piping, or the tips can be worn away by particulate in the gas stream. If tip wear is persistent, tips can be made of extremely-hard, exotic alloys.


Uneven air flow: Improper design of air boxes can cause uneven air flow. This will be seen most often with forceddraft burners. Warped floor: Heat damage to the floor of fired heaters and furnaces (or to walls of wall-mounted burners) lead to incorrect burner positioning. Header piping not sized properly: Under-sized gas header piping causes a large pressure drop that reduces gas or air flow to the burner. Broken or missing refractory: Refractory tiles of burners stabilize the burner flames. If tiles are missing or broken and out of position, they will not absorb and radiate heat properly, which can distort the burner flame.

Sparklers in flame Water in gas: Condensation of water in the gas header will be indicated by sparks in the flame. Wet steam: Condensate in steam lines on atomizing oil burners will cause small, bright sparks in the flame. Poor atomization: The larger the oil droplet, the slower it burns (if it burns).

Unstable gas flame High air flow: Too much air tends to blow out the burner flame. Mis-positioned tips: Incorrect tip placement due to incorrect burner mounting or warped floors will affect the ability of burner tiles to stabilize the burner flame. Liquid carry-over: Slugs of liquid will bring too much fuel to the burner. If the liquid burns on the tip, it will greatly accelerate corrosion of the burner. Improperly installed or designed flame retention device: Some burner designs use baffles to prevent air flow from blowing out the burner flame. Others, like most NAO

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burners, use burner block to absorb and radiate heat to stabilize the combustion flame. Missing flame stabilizers: Raw gas burners have flame retention devices to prevent the flame from blowing off of the burner tip. Some burner designs have flame retainers that are metal baffles that can corrode and break off, leading to unstable gas flames.

Unstable oil flame High or low oil temperature: Burners are designed for specific fuel conditions. If these conditions are not met, combustion may not be stable. Overheated oil gun: Overheated oil guns cause pulsating flames. High steam flow: Oil and steam connections reversed: Water in oil: Slugs of water displace fuel and snuff the flame. Improperly installed or designed flame retention device: Some burner designs use baffles to prevent air flow from blowing out the burner flame. Others, like most NAO burners, use burner block to absorb and radiate heat to stabilize the combustion flame. Pump cavitation: Pulsating fuel flow causes unstable combustion. Pulsating pressure pump: Pulsating fuel flow causes unstable combustion. Leaky purge (by-) valve: Steam or inert gas in the oil line can be caused by leaking or open purge valves. Improper forced-draft fan turndown: Over-sized air blowers surge at low flow rates. Under-sized blowers cannot provide adequate air at high fire rates.


Carbon build-up on oil gun Incorrect positioning of gun: Mis-alignment of the oil gun can cause the oil jet to touch the burner block. The block prevents the proper atomization of the oil where it burns (partially) and forms carbon. Poor atomization: Poor atomization causes oil to dribble on the oil gun where it burns and forms carbon. See the section on poor atomization for more information.

Corrosion & Erosion Vanadium, sulfur, or sodium in oil: They corrode the metal of the burner tips, standpipes, and housing, and they corrode the refractory lining and metal structure of the heater. If the problem is persistent, exotic alloys can be used on the burners that are resistant to the corrosive effects of vanadium and sulfur, but this does not protect the furnace tubes. The adverse effect of vanadium on the furnace tubes can be partially counteracted by lower the tube metal temperatures. Except for furnaces operating with exceptionally high tube metal temperatures, vanadium content of 20 ppmv or less are normally not of concern. Sodium is an equally serious problem in heaters, though desalting the crude will generally eliminate this concern. Solids (sand, grit) in fuel: Over time, solid particles wear away the burner tip. This is the result of missing strainers or strainers that are too coarse. Poor material selection: Among other things, H2S reacts with carbon steel piping to form a yellow powder that can plug tips and other orifices.

Burner shuts off automatically UV detector doesn't see flame: The UV detector may be improperly aligned, or the lens of the scanner is blocked. UV detector reads pilot spark as flame: The UV scanner does not need to target the pilot nozzle. The burner pilot flame should be several inches taller than the pilot nozzle.

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Solenoid valves backwards: If the fuel gas to some burners shuts down automatically as the firing rate is increased, check the direction of the solenoid valves. If the valve is backwards, it may function under some flow conditions and shut down suddenly under others.

Low heat release Change in fuel gas: If the new fuel gas has a lower heating value, the overall heat release will be lower under the same gas flow rates. Too much or too little air: Too much air takes additional heat as it es through the furnace. Too little air allows some fuel to through the furnace without burning. Low gas flow: Restrictions at the burner will result in low flow at proper pressures. This may only be evident by low heat release.

High burner heat release Burners over-fired: High gas pressure results in high gas flow and excessive heat release that can damage a heater or furnace. Oil and steam connections reversed: Pushing oil through the steam nozzle will allow for higher oil flow, yielding a higher heat release. Worn tips: Tip wear increases the drilling size, which increases the fuel flow through the tips. Low excess air: The hottest combustion flame is at stoichiometric conditions. Excess air ensures complete combustion, but it also reduces flame temperature. Burner block or tips out of position: Mis-alignment of the burner creates distorted flames that can cause pockets of high heat in the furnace or heater. Over-pressured furnace: High furnace pressure holds products of combustion in the furnace longer and can reduce excess air flow.


Insufficient draft Stack damper (partially) closed: This causes a restriction in the stack that reduces the flow of combustion air into the heater. Blower wired backwards: Forced-draft fans only operate at a fraction of their rated capacity when they operate backwards. Excessive furnace leaks: Tramp air, excess air that enters through leaks in the furnace floor and walls, cools the products of combustion and reduces their buoyancy. The draft caused by the chimney effect is then reduced.

Too much draft Stack damper wide open: Stack dampers restrict flow out of the furnace. Air s close improperly: Air s may be stuck fully open. Under-firing forced-draft burner: Under firing the burner means that the blower controls are not reducing air flow to the burner to match a reduction in fuel flow.

Flashback Gas flow too low (on pre-mix burner): Low gas flow on a pre-mix burner slows the velocity of the air/gas mixture through the burner nozzle. If the velocity drops below the flame speed, flashback occurs. Pockets of hydrogen in refinery gas: The flame speed of hydrogen is significantly greater than methane or propane, the primary constituents of refinery gas. Venturi (of pre-mix burner) overheats: Heating the venturi or other piping of a pre-mix burner due to damaged

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insulation or due to absence of coolant may raise the gas/air mixture above its auto-ignition temperature.

Smoke and CO formation Too little (or too much) air: Lack of oxygen prevents the complete combustion of fuel. Too much air can quench the flame before combustion is complete. Over-fired oil gun: Too much fuel makes complete combustion impossible. Low oil temperature: Improper pre-heating of oil reduces combustion efficiency that can lead to smoke and CO. Oil and steam connections reversed: Oil is improperly atomized so combustion is incomplete. Also, oil flow through the steam side of the oil gun is excessively high.

High NOx formation High furnace temperature: NOx formation is a function of temperature. The higher the flame temperature, the higher the NOx formation. High fuel-bound nitrogen: Firing burners at low excess air eliminates most of the nitrogen that can form NOx, however nitrogen entering burners through fuel cannot be eliminated. High hydrogen content of fuel gas: Hydrogen burns hotter than other gases. Switch fuel from gas to oil: Oil produces more NOx than gas, in part because of fuel-bound nitrogen. High intensity combustion: High intensity combustion caused by flow swirling and vorticity increases the heat density and temperature of the flame.

Noise (resonance) Unstable combustion flame: Distorted and unstable flames generate low frequency noise.


Resonance of piping: Resonance of nozzle-mix burners or of steam injection can generate high frequency noise. Oversized air dampers that are almost completely closed may cause cavitation of air flow past the damper.

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References Chemical Engineering Progress. January 1994

For Additional Reading Bitterlich, G. M. The NOx Enigma discusses the factors contributing to NOx formation using emperical data collected from NAO burner testing. Ask for RP77-14. “Burner Noise and Its Suppression” is a technical report by NAO that analyses and relates the effects of fuels, firing rates, and burner design on noise. Combustion Tips, Volume 1, Number 4, “Lo-NOx Burners reduce nitrogen oxides to acceptable levels” reviews the newest feasible technology for reducing NOx in burners. “Fire Simulation Systems” is a four-page piece of NAO literature with photographs and descriptions of the many fire simulation systems we have provided in the past few years.


Air Heaters — Property of NAO Inc.

Air Heaters NAO has designed and fabricated Air Heaters for many years. The first NAO unit was made around 1933 for a company in Chicago called UOP (Universal Oil Products), which is involved with various process designs using air heaters. Currently, we have a large air heater for a UOP process for Foster Wheeler in New Jersey; the final is Fina in Port Arthur, Texas. This unit is 9 feet in diameter, 42 feet long and has an operating pressure of around 150 psig. The Fina unit fires about 80 MMBtu’s of heat. We have made a larger one for a company called Llanoven in Venezula that had a firing rate of about 150 MMBtu’s.

Operating Temperatures Normally, air heaters operate at fairly low temperatures, 1,400 to 1,500 °F. We have produced air heaters for temperature ranges from 200 to 2,800 °F. However, few air heaters get as hot as 2,800 °F, though high temperature heaters are easier to make. Low temperature air heaters require a lot of by air. By air dilutes the extremely hot combustion products of the air heater burner. It also tends to make the burner flame unstable, sometimes quenching the flame, unless the heater is designed properly. We recently built a High-temperature Air Heater for Valero Petrochemical in Corpus Christi, Texas. It was designed for 2,700 °F—very hot air. Valero’s application was to heat a flue stack so that they would get more lift (from the buoyancy of the gas inside) and to prevent the formation of condensate. They had scrubbers on their stacks to reduce emissions of sulfur compounds that form acid rain, but the scrubbers reduced the flue-gas temperature, producing condensate. Injecting very hot air from our air heater raised the temperature and eliminated the condensate. Our unit replaced an existing Brand-X Air Heater that had corrosion problems: The moisture that the heater was supposed to eliminate was being thrown into the air heater, where it destroyed the metal integrity of the housing.

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Lower temperatures are used for drying grains and tobacco. We recently sold an induced draft unit to FMC Corporation to be used as a dryer. This unit operated at a very low temperature—300 °F to 400 °F. The lower temperature air heaters can also be used for drying cement and for freeze prevention. Customers use them for airplanes in hangers and to dry out boilers and furnaces after repairs.

Air Heater Pressures Air Heaters generally operate in one of three ways: Forced Draft, Natural Draft, and Pressurized. Forced-draft Air Heaters rely on fans or blowers to supply air to the burner and by. The fans push the heated air through the Heater to the vent stack or drying area where it is needed. Forced-draft Heaters operate at positive pressures up to 2 psig. Natural-draft Air Heaters are preferable to forced draft, if they are applicable. Natural-draft heaters do not require the additional capital or operating expense of fans and blowers. An natural-draft air heater will have two openings with dampers: One opening will supply air to the burner, the other will supply air as a by. Natural draft relies on the buoyancy of the hot combustion products to draw air into the heater. These heaters operate at slightly negative pressure—from -2 to -6 inches of water column (-5 to -15 mbar). Pressurized Air Heaters are less common than natural or forced draft heaters. Pressurized Air Heaters can be made to supply heated air at up to 150 psig. With pressurized air heaters, the ignition system must be designed particularly well. Standard spark ignitors for burners do not work at pressures over 3 psig. NAO has a High-intensity Spark Ignitor that has been tested at pressures up to 3,000 psig.

Portable, Rental Air Heaters There are a number of regulations developing in the United States for ships and tank trucks, requiring them to be cleaned after each use. Portable air heaters would be ideal for blow-drying them so that the ship or truck can return to


service as quickly as possible. These can be skid-mounted or trailer-mounted units. NAO has the capability rent these types of portable air heaters. They actually haven’t been built yet, but they can be quickly assembled to meet a customer need.

Excess Air vs. Heater Temperature This chart approximates the effect of excess air on the hot mix temperature for any burner. The actual value will vary slightly for differing fuel compositions.

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Sprayers — Property of NAO Inc.

Sprayers NAO has a very large market share of all the Process Sprayers. We probably sell about 90 to 95% of them—a nice piece of business! The sales per year fluctuate up and down, but we often sell as much as a half-a-million dollars of sprayers each year. We have only one main competitor, Brand X, but they have only a small part of the market. Process Sprayers are used mostly to spray water for quenching or scrubbing. They also spray oil for cat cracker start-ups, and they spray various chemicals for scrubbing or for process units. These sprayers handle up to 3,500 gallons per hour, even at very high pressures. In one application, we supplied a sprayer for coal gasification at 1500-psi reactor pressure—we had to have a winch on the gun to prevent it from flying out and causing injury or damage.) Many times, sprayers handle very heavy chemicals that have sand and other solids in them, so the tips will tend to erode. There is quite a bit of replacement business here. To help reduce wear, we often make the tips out of exotic materials such as Hastelloy or Stellite. Stellite is a very hard material. It is almost impossible to drill or machine, so we essentially have to cast the tip with the holes or the slots right in it. If a sprayer must be removed for cleaning or repair, you must loosen the packing gland, so the sprayer gun will retract. When you’ve opened the packing gland, you can close the sprayer valve and remove the sprayer for inspection, maintenance, or cleaning.

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Sprayer Applications Production and processing •

• • •

Spray drying of dairy products, coffee and tea, starch pharmaceuticals, soaps and detergents, pigments, and other products Spray cooling Spray reactions, such as absorption and roasting. Atomized suspension liquids such as effluents, waste liquors, etc.

Treatment • • • • •

Evaporation and aeration Cooling of spray ponds, towers, and reactors Humidification and misting Air and gas washing and scrubbing Industrial washing and cleaning

Coating • • • • •

Surface treatment Spray painting Flame spraying Insulation, fibers, and undercoating materials Particle coating and encapsulation

Combustion • • • •

Oil burners in furnaces and heaters Diesel fuel injection Fuel injection on gas turbines Rocket fuel injection

Miscellaneous • • • • •

Dispersion of chemical agents Agricultural spraying of insecticides, herbicides, fertilizer solutions, etc. Foam and fog suppression Printing Acid etching




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Refractory — Property of NAO Inc.

Refractory Refractory materials serve one of two purposes. In some applications, the purpose of refractory is to act as an insulator. Insulating refractories shield the metal walls of process equipment from the corrosive effects of products of combustion at elevated temperatures. In other applications, the purpose of refractory is to collect and radiate heat. In fired heaters, furnaces, thermal oxidizers, and other combustion equipment, the ability of the refractory to store and radiate heat insures a stable, uniform flame. In most applications, refractories serve the dual purpose of insulation and flame stabilization. Every application has specific requirements that can be met by a wide variety of refractory products. There are a wide variety of refractory and insulation products available. Their significant properties include: • Ability to maintain strength under high-temperature conditions • Cold crushing strength—impact strength at lowtemperature operations and the ability to withstand handling and shipping without damage • Modulus of rupture—a standard measure of structural strength provided by load testing • Insulating value—the ability to provide resistance to the flow of heat • Porosity—the susceptibility to penetration by slags or gases • Erosion—the physical deterioration of material due to with gases, liquids, an solids on the hot face • Corrosion—the chemical process that destroys the refractory bond or the chemical integrity of the insulation. Of particular interest is the operation of refractory in an oxidizing or reducing atmosphere. A reducing atmosphere, one deficient in oxygen, will tend to degrade refractory material containing iron or silicon components. • Thermal expansion—the reversible change in linear dimensions under heating and cooling. Where refractory is used as a liner in a flue, the expansion of the refractory must be evaluated with respect to thermal expansion of the flue.

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Castable Refractory Castable refractory, sometimes called refractory concrete, is supplied dry, to be mixed with water before installation. It is installed by pouring (casting in place), troweling, pneumatic gunning, or ramming. A castable refractory provides a smooth, continuous, monolithic mass. Castable materials are normally placed in a mold or in an area prepared with pins, mesh, or other anchor devices to hold the refractory during placement and curing. Mesh, grid, studs, or needles may also be used to enhance the strength of the refractory installation. Castable refractories are classified as dense or lightweight (insulating). Dense castable have excellent mechanical strength and low permeability. Their insulating properties, however, are relatively poor. As dense materials, over 100 lb/ft3, they offer good resistance in wet service such as quencher linings. Lightweight castables are excellent insulators. All castable materials have the advantage of placement in irregular areas such as furnace transitions and burner openings. They are cast in place. Poured castables require a form. Plastic castables must be rammed in place. Gunned castable is blown in place and forms are not required. The use of gunned material, however, is often dictated by the size of the job in question. Gunning requires installation equipment including air compressors and gunning applicators that would be un-economical to provide when compared to the relatively small amount of equipment needed for poured or plastic castable installation. Normally, gunning is not economical for jobs less than a week in duration. The quality of a castable installation is a function of mixing, curing, and application. Mixing must be performed to the refractory manufacturer’s instructions. If the amount of water added is not within the product specifications, the castable refractory will be weak when curing and when in service. A dry mix will not flow into its form properly and voids will appear. A wet mix will promote segregation of the mix as it solidifies and cures, providing inconsistent and poor refractory quality. Note that poured refractory is often vibrated to aid its flow, similar to the placement of concrete. Vibrating eliminates voids, but excessive vibration (longer than 30 seconds) will promote segregation of the mix.


Curing refractory is necessary to set a ceramic bond, creating the strength of the refractory matrix. Without proper curing, the refractory will not develop mechanical strength or chemical resistance (to corrosion). Refractory is usually either air-set or heat-cured. Air setting requires only a quiescent period where the refractory is not subject to mechanical changes (motion) or heating effects. Heat curing requires the refractory to be heated at a controlled rate to establish the ceramic bond. This bond may require that temperatures of 1,000 to 3,000 °F be reached and maintained. Often incinerator temperatures are not high enough to cure heat-setting refractories, and special operating procedures are necessary to bring the equipment to the curing temperature. Most castables used in furnaces and heaters today are air set. Castable refractories are manufactured at NAO’s Environmental Research & Service Center in Texas. NAO has a large inventory of burner block and encased block tiles. Burner Block, also know as Muffle Block, are the “bricks” that are in the furnace floor. Gas burners fire through a ring of block tiles and heat them up. The block radiates heat and stabilizes the burner flame. Encased Blocks are a variation of the Muffle Block used with oil guns. Rather than sit in the furnace floor, Encasements have a metal shroud that allows them to bolt to the burner housing. Encasements surround and stabilize the oil flame, and they are surrounded by Hexad gas burners. With our huge stock of molds, we can provide cast burner blocks for all NAO units, and, if provided a drawing or a sketch, NAO can easily make molds and produce the various blocks for any competitors unit. If necessary, we have a kiln to cure and dry the cast block prior to shipment, if the customer so chooses. We have also worked with third-party testing services to qualify our castable products prior to shipment.

Plastic Plastic is sometimes referred to as a castable material because is can be formed to any shape. Plastic refractory is

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a soft refractory that can be hammered into place. It is often placed and packed on the walls of a heater a fired under controlled conditions when refurbishing old equipment. This is a cost-effective substitution to gunning a castable when jobs are small.

Firebrick Brick is formed by pressing castable refractory into a mold. It is slightly more dense than plastic, and it is pre-fired and shipped in a ready to use form. Conventional firebrick is kiln-baked to uniform, controlled consistency and quality. The term firebrick refers to dens brick, over 100 lb/ft3, normally placed in direct with the hot gas stream. It has relatively poor insulating quality. Insulating firebrick (IFB) is a lightweight, porous brick, normally less than 50 lb/ft3, that can be placed in direct with the gas stream and that provides good insulating characteristics. IFB is machined to its final shape, providing excellent dimensional control as compared to firebrick which is used as cast. IFB is lower in strength than firebrick and, because of its porosity, is a soft material not effective with erosive gas streams—gas streams with high particulate components. IFB’s low abrasion resistance limits the maximum velocities allowed adjacent to it. Where refractory brick is required to have high abrasive resistance and insulating value, firebrick will often be provided with insulation block as back-up between the firebrick and the furnace-flue wall. Anchors are normally provided to hold brick in place. Firebrick and IFB are both self-ing. However, because of the relative structural strengths of these materials, IFB requires a more elaborate anchoring system than firebrick. Brick manufacturers each have their own unique anchor and anchor system design.


Ceramic Fiber NAO uses ceramic fiber blanket as an insulating material on thermal oxidizers and ground flares. This is significantly cheaper than fire brick (which we once used) and it works better. Ceramic blanket has a density of about 5 lbs/ft3, about 20 times less dense than castable refractory and fire brick. This allows the oxidizer to heat up quickly on start-up and to react quickly to changes in the flow stream. This reduces assist gas demand and saves money. Firebrick insulation, on the other hand, requires a lot of time to heat up, and it reacts slowly to process changes. If the flow of vapors to a thermal oxidizer increases suddenly, a ceramicinsulated combustion chamber will quickly heat up and compensate for the change, reducing fuel costs and improving combustion efficiency. A firebrick chamber will require more time and more assist gas to heat up; in the mean time, harmful vapors are moving through the chamber un-combusted. Ceramic fiber also comes in vacuum-formed shapes. It’s characteristics are similar to ceramic blanket, only it is slightly more dense. The ceramic fibers are pressed into a shape, usually a hollow cylinder for our purposes. NAO uses vacuum formed ceramic fiber in small thermal oxidizers.

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References Brunner, Calvin R. Handbook of Incineration Systems. McGraw-Hill, Inc. 1991.



Flares — Property of NAO Inc.

Flares Flaring is a high-temperature oxidation process for disposal of waste gases and vapors during normal operations and emergencies. Flares are used for the quick relief and effective elimination of excess process streams due to unexpected equipment failures or major plant emergencies, such as instrument malfunction, power failure, or plant fires. Prior to the utilization of process flares, gaseous waste streams were vented directly to the atmosphere. Venting created health hazards and safety hazards. Health hazards occurred when toxic vapors reached the ground where plant personnel worked. Safety hazards occurred when combustible vapors reached the ground where they could be ignited. The resulting explosions and fires had devastating consequences for operating personnel, the surrounding neighborhood, and the plant itself. Flaring is a solution to these hazards (though flaring does present its own problems of heat, smoke, light, and noise). Burning the waste vapors in a flare converts the pollutants into less-noxious components. With proper combustion design, all of the components of the waste stream will be converted to carbon dioxide and water vapor with few secondary pollutants. Flares are primarily used in the oil and petrochemical industry, from oil production through transportation, storage, refining, processing, and distribution. Flares are seen on offshore platforms, at propane (LPG) and natural gas (LNG) terminals, along hydrocarbon pipelines, in refineries, at storage terminals, at steel mills, and at petrochemical plants. However, their use and importance is not limited to these applications. Flares are used for sewage digesters, coal gasification, rocket engine testing, nuclear power plants, heavy water plants, and ammonia terminals. These flaring applications require three general types of flares to insure high operating performance and efficiency. The least complex and most limited design is the nonsmokeless flare, sometimes called the utility flare. It is used

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for hydrocarbon and vapor streams that burn readily and do not produce smoke.

Non-Smokeless Flare Applications • • • • •

Methane Hydrogen Coke-Oven Gas Carbon Monoxide Ammonia

Heavier hydrocarbons can be flared using a non-smokeless design, but only with considerable smoking and lower combustion efficiency. This may be tolerated if flaring occurs only infrequently during short, emergency upsets. A second type of flare, the smokeless flare, is often used for heavy hydrocarbons for clean, efficient disposal of the entire waste stream. Smokeless flares are required for any paraffin above methane and for all olefins, di-olefins, and aromatics. They are also used for coke-oven and coal-gas streams where tar particles or tar-laden vapors are present. These flares use outside momentum sources—steam, highpressure fuel gas, water injection, high-velocity vortex action, or air blowers—to provide efficient gas and air mixing and turbulence for smokeless operation and improved combustion performance. A third type of flare, the endothermic flare, is used for lowheat-content waste streams and toxic vapors. This unit is called an endothermic, or fired, flare because it provides additional energy to the waste stream for complete oxidation. As a rule of thumb, whenever the heat content of the waste stream is below 100 Btu/ft3, then a fired flare with an assist gas must be used to insure complete oxidation of the waste. (Recently, NAO developed a waste gas combustion unit that was field tested to flare waste gas at 55 Btu/ft3 with no assist gas.) In the design of any flare, many critical factors—e.g. radiation, noise, and dispersion—must be considered and resolved in order for the flare to be operated safely. Less critical, but equally important, operational design factors— e.g. combustion efficiency and flame stability—must be

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considered for the system to be considered environmentally acceptable.

Critical Design Factors of a Flare System • • • • • • •

Thermal Radiation Liquid Carry-Over Noise Dispersion Pressure Drop Visible Light Explosion Hazard

Operational Design Factors of a Flare System • • • • • •

Combustion Efficiency Flame Stability Positive Piloting Reliable Ignition Effective Air Entrainment and Mixing Maintenance

Resolving the many design factors is not sufficient to insure a safe and reliable flare. The possibility of mechanical and operational problems must be anticipated. A competent flare designer will be able to handle factors such as flame stability, but the designer must also be able to cope with the high-temperature problems associated with the close proximity of the large flare flame. Maintaining flame stability for varying flow rates and compositions is essential if the flare is to serve its principal purpose of waste gas combustion.

The Fluidic Flare Some basic rules for proper flare mechanical design should always be observed: No moving parts, No burning inside the tip, and No small openings for steam or gas injectors. The NAO Fluidic Flare satisfies these requirements.

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Among other things, the Fluidic Flare has the patented nomoving-parts multi-baffle Fluidic Seal to prevent burning inside the tip, and it has the patented VorTuSwirl Vanes at the tip to retain and stabilize the flame. NAO’s VorTuSwirl take approximately 30% of the gas flow and swirl it in a vortex. (The remaining 70% goes straight up and that makes your main flame.) With the swirling effect around the outside, the flame is stabilized at velocities approaching sonic velocity. With natural gas, which is mostly methane, sonic is a velocity is approximately 1200 feet per second, or about 900 miles per hour. With most conventional flare tips, on the other hand, less than half of this performance can be obtained; with no flame retainer at all, the exit velocity is restricted to two-tenths of sonic, or about 250 feet per second for methane. If you have an older type of flame retainer such as a bluff body, then you can go to half of sonic, around 600 feet per second. Higher exit velocities all for more stable flare flames during high wind conditions, making the NAO Fluidic Flare the most reliable flare tip on the market. With NAO, you have the best technology currently available for flaring. Located around the outside of the Fluidic Flare is a combination wind-and-heat shield—the conical windshield. The pilots actually protrude through the wind shield, so that they are protected from the combustion flame. This is especially important for the small piping of the pilots which is susceptible to being burned up and destroyed on a conventional flare. This next photo depicts an NAO Clear Glow Fluidic Flare (NFF-CG). This flare was supplied to BP for an LPG terminal—the Solem Vough installation. It replaced several different flares. At this terminal, they have a difficult situation with a maximum flow of 130 metric tons an hour and a total pressure drop of about 100-mm (4") of water column during emergency situations. Most of the time, however, they flare only about 5 tons an hour, a very small percentage (3%) of the overall waste gas with a pressure drop of just a fraction of a millimeter. As a result, the normal exit velocity is only a few feet per second. At the Solem Vough installation, a small island on the northern tip of Scotland, they have very severe winds all the time. It is common to have winds of 50 or 60 mph at grade level. Since this flare tip is on a 200 foot stack, it

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experiences hundred-mile-an-hour winds all the time! Before our NFF-CG was installed, BP tried several vendors, none of whom could supply a tip that would last longer than three or four months. They had a flare manufactured by Company X that failed within three months. They tried a flare from Company D, and it also quickly failed. They tried a flare from Company I that had a wind shield with slats that failed within four months. And they tried an old-type NAO flare, an NCG, with a picket-fence wind shield around the outside. It failed within four months. We thought the best way to really test the new technology of the Fluidic Flare was to give BP one to try. It has been in service now for almost 10 years and it is still going strong! The conical wind & heat shield is now a little bit warped because it has seen a lot of heat, but the shield isn’t a structural member so it doesn’t really matter if it gets bent and distorted. Without the NAO conical wind shield, the flare body warps under the heat—even refractory-lined flare bodies will warp—until, inevitably, the metal of the flare body completely disintegrates and you are left with a “burned-up” flare tip that must be replaced. We gave BP a flare tip back in 1979 because we had only two NFF Fluidic Flares installed at the very southern tip of Argentina, and we had no real back then on how they were working. We decided the best approach was to give BP a Fluidic Flare for this worst-case installation; and if it worked there it would work anywhere. That has proven to be the case. The NAO Fluidic Seal is covered by two patents: The first covered a multi-baffle seal down inside the body of a flare tip (the NCG). A more recent patent is for the Fluidic Seal at the top (the NFF). Both patents cover one or more baffles, so if a competitor puts even one baffle near the top of a flare they will be infringing on NAO’s patented design. Also, if they put more than one baffle inside a flare tip, anywhere, they will also be infringing. NAO now makes several types of Fluidic Seals, including insert types or segment types that fit into customer’s existing flares. The Fluidic Seal works by using baffles of the seal and the flow of the purge gas to push air out of the tip. Gas flows unrestricted in the “upward” direction. Flow through the

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Fluidic Seal is about five times more difficult when moving in the “downward” direction, so air tends not to move down into the stack. NAO has physical models you can use that really illustrate how the unit works. Bulletin #38-A provides many more details about the NAO Fluidic Seal. The NAO Fluidic Flare has been used in many applications around the world in horizontal, vertical, and angled installations, onshore and offshore. For more information on flare applications, see the section titled Applications in this section.

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10 Reasons for Selecting the NAO Fluidic Flare 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

Patented no-moving-parts Fluidic Seal Reduced Purge Gas Consumption Fluidic Seal eliminates burning inside tip Conical Windshield Prevents Flame Lick Flame Retainers keep Flame Erect, insure Turbulence, and Reduce Smoke Higher Exit Velocity of gas insures Stable Flame in Mixing Zone Minimum Profile reduces Wind Loading, which reduces capital cost Energy Conservation Pilots save Money Conical & Pilot Windshield Protects Pilot Flame under any wind condition NAO Fluidic Flare Systems are field proven to Outperform the Competition

The Molecular Seal To the right is a conventional flare tip with a molecular seal. The molecular seal works by allowing heavy gas molecules to sink to the low point and light gas molecules to rise to the high point. These layers of molecules “seal” the stack from air ingress. Unfortunately the molecular seal does not become effective until the first bend. This allows burning inside the molecular seal, because the ambient air is as heavy or heavier than the purge gas. The purge gas tends to flow out, the air tends to sink back in, and combustion flames move up and down inside the molecular seal. Depending on the location of the seal on the flare stack, you can actually get burning, almost 30 feet down inside of the flare. Keep in mind that a molecular seal is made of carbon steel which tends to “burn.” We call this phenomenon “cancer.” This cancer is hidden, and it is gradual deterioration; but eventually a flame will shoot out through the side of the molecular seal or the internals of the seal will corrode away. Hence, the molecular seal is a major problem. The only advantage of a molecular seal is that, because it is a gravity-type of seal, if you lose purge gas (which is very unlikely) a molecular seal will continue to function. Unless,

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of course, the gas in the flare stack is hot, in which case it will contract due to temperature changes, thus drawing air past the seal. Most plants around the world have accepted the Fluidic Seal because they realize it is very unlikely that all purge gas will be lost. More often, there is on-going leakage of gases to the flare system, so some purge flow never stops. , the purge rate for a Fluidic Seal is typically about three-hundredths of a foot per second (0.03 fps, 0.2 mph, 1 cm/s). With no seal at all, the purge rate increases to about a half-foot per second. Otherwise, burning occurs inside the tip and ruins the flare. To satisfy customers that want all the benefits of the Fluidic Seal with the additional security of the gravity seal, NAO has developed a MoleFluidic Flare (Molecular Fluidic) in which the molecular seal is built into the flare tip. Since the molecular seal is located at the exit of the flare tip, it is acts as a Fluidic Seal by preventing air from coming down inside the tip.

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Sizing a Flare It never pays to oversize a flare. An oversize flare requires more pilots, more pilot gas, and more purge gas, and an oversized flare receives more heat exposure because the flare flame at low flow is closer to the tip which overheats the metal and reduces flare life. Surprisingly, flares are still being “oversized” to handle future capacity of a plant expansion. For example, the ultimate plant capacity may require a 54-inch flare, though at present the plant is limited to only half of capacity—requiring a 36-inch flare. By building a 54-inch stack and installing a reducing cone and 36-inch flare tip with a gas seal, one flare pilot will be eliminated, the purge gas requirement will be significantly reduced, and the flare tip life will be extended. Depending on the size of the flare, this concept should be considered whenever a complete flaring system is engineered for future capacity requirements. Normal, continuous flow rates to most process flares are usually quite low or non-existent. Many times, the normal flow to the flare is a purge flow to keep air from moving down the stack. Although the normal, continuous purge flow may not produce a visible flame, they can consume substantially more energy than the spectacular (and rare) major-emergency flare flows. Methods of controlling and reducing such continuous energy requirements should be considered for cost-efficient performance and overall reliability. Proper operating procedures are also important in flare-energy conservation.

Flare Design Factors • • • • • •

Tip Diameter and Pressure Drop Thermal Radiation Liquid Carry-Over Air Entry Combustion Efficiency Reliable Pilot and Ignition

General factors influencing a safe flare design are sizing, pressure drop, radiation, liquid carry-over, combustion efficiency, air entry, and reliable pilots. All of these factors

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but radiation and carry-over also relate to the cost-efficient performance of a flare.

Tip Size and Pressure Drop Accurate flare sizing is required to ensure safe operation. Sizing is dependent on flow rate, gas composition, gas temperature, and available pressure drop. Of these, flow rate and pressure drop are most critical for flare performance. A reasonable estimate of these two criteria must be determined. If the flow rate is greatly overestimated and an oversized flare is specified, burning inside the flare tip will occur and the tip life will be greatly reduced. The flame of an oversized flare is very lazy and is easily affected by cross-wind. Wind will cause the flame to tilt, which results in higher radiation levels and reduced flare life due to flame lick. Serious underestimation of the flow rate or pressure drop of the flare will result in poor flame stability. The flame may lift off and blow out, releasing unburned hydrocarbons into the atmosphere. For typical open-ended pipe flares, the maximum exit velocity of the gas must be limited to 20% sonic velocity to prevent flame-out. Modern commercial flares use flame-retention devices to stabilize the flame at velocities up to 50% sonic velocity. A typical device consists of an annular ring with many small piloting holes surrounding a large central orifice. Current flare design technology permits the use of smaller flare diameters with higher exit velocities and shorter stacks and booms. In this way, flaring is accomplished with less flame tilt and thermal radiation, and the tip life is extended.

Thermal Radiation The emergency burning of large quantities of hydrocarbons in an open flare is a source of extreme thermal radiation many times that of solar radiation. This radiation level must be determined to ensure the safety of operating personnel and surrounding equipment. Sometimes, environmental effects of thermal radiation must also be considered—flare installations located on permafrost, for instance. For a

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complete summary of thermal radiation, see the related section in this chapter.

Liquid Carry-Over Since flares are designed only for gas service, the dumping of liquid into a flare can be catastrophic. The amount and the extent of damage depends on the quantity of liquid hydrocarbon going to the flare, the wind speed, the wind direction, the flare-gas exit velocity, and the proximity of the flare to personnel and equipment. Small liquid-hydrocarbon particles can be burned in a flare, but their size is critical. Particles with sizes up to 90 microns will be burned within the flare flame and go unnoticed except for a slight change in flame color and an increased tendency to smoke. When the particle size approaches 150 microns, burning droplets outside the flame will be clearly visible, even in daylight. These particles will not normally reach grade level, except for short flare stacks (heights under 10 meters). The exact trajectory of the droplets depends strongly on wind speed, and should be calculated for critical locations. Droplets larger than 150 microns will result in burning rain reaching grade level or the platform work area. This burning rain can injure operating personnel, scorch steel equipment, destroy instrumentation and electrical wiring, an ignite anything combustible at grade level. A liquid spill-out of a flare tip will usually result in some hydrocarbon running down the side of the flare. Alloy components of the flare will not be seriously affected, but the carbon-steel stack can be destroyed. Knock-out drums, or disentrainment drums, are used to eliminate liquid carry-over. Knock-out drums use the settling effect (for low flow rates) and cyclone action (for high flow rates) to separate liquid particles from gas flow streams. For more information on knock-out drums, the related section in this chapter.

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Air Entry Air entry into the hydrocarbon-filled stack could result in an explosion of the flare stack. There are two paths of air entry into a stack. One is through leakage in the system at low flow; the other and most direct path is down the flare stack through the tip. A continuous flow of purge gas is used to prevent air penetration down the stack. If the flare stack contains a low-density waste gas or purge gas at low flow rates, then the frictional pressure drop of the flare stack is less than the buoyant draft of the gas. The result is negative pressure at the base of the flare stack. Any leakage of connections, flanges, or manways could then produce an explosive mixture in the stack that can be ignited by the flare pilots. The best solution to the air leakage problem is a tight flare header and stack with a reliable oxygen monitoring and alarm system. A continuous oxygen monitor will indicate oxygen (air) levels in the stack. This automatic system will eliminate the need for maintaining high purge rates to maintain back pressure and keep the stack pressure positive. The result is significant energy savings, even for smalldiameter flare systems. Exact energy savings will depend upon the diameter & height of the stack, the molecular weight & temperature of the purge gas, and the explosive limits of the purge gas. Amazingly, some flare lines are still continuously maintained under positive pressure! With proper flare monitors and effective controls, the need for excessive purge-gas flow rates is eliminated. To further reduce purge gas requirements, consider the use of a Fluidic Seal and/or purge-control systems. A Fluidic Seal can reduce the purge rate by 25-95%.

Gas Seals To reduce the likelihood of air moving down the tip into the stack, gas seals such as the molecular seal or the Fluidic Seal are used. The NAO Fluidic Seal uses cone-shaped baffles to reduce the depth of air penetration at the tip of the flare. The baffles increase the velocity of the purge gas and push air out of the tip. The Fluidic Seal and molecular seal are described in detail previously in this chapter.

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Inert Gas Purge With the present trend toward bigger flares, inert-gas generators can offer a fast pay-back and significant yearly savings. For purging applications, expensive water-cooled generators are not required. The inert gas can be air-cooled to warm temperatures within stack design tolerances, or it can be circulated to a water seal (to prevent freezing) or a knock-out drum (to prevent condensate). NAO has developed a complete line of inert-gas generators specifically designed for flaring applications. Typical composition of the inert gas is 87% N2, 12% CO2, and less than 1% oxidizing or reducing residuals. Typically, one cubic foot of natural gas can be converted to nine cubic feet of inert gas. With proper installation of an effective gas seal and automatic start-up and shut-down control of the inert-gas generator, the total energy savings can be substantial. NAO also has developed an inert gas generator using the latest in membrane technology. These rely on membrane filters to separate atmospheric nitrogen and oxygen. These units efficiently generate 97% pure N2 inert gas. These can be installed remotely and only require electric utilities. These can easily be supplied with storage pressure vessels to maintain purge flows in case of power failure.

Combustion Efficiency In refineries and petrochemical plants, smokeless operation is necessary to ensure complete combustion of the heavy and unsaturated hydrocarbon vapors. Generally speaking, complete combustion means that flares must operate at 98% combustion efficiency, or better. This applies to continuous flaring applications required to satisfy government regulations. In the United States, if an open flare has a waste gas with a heating value of 300 Btu/ft3, and exit velocity not exceeding 60 ft/sec, and no smoke is visible, it is assumed that combustion efficiency is 98%. Unfortunately, there is not currently a method for continuous monitoring of open-flare combustion efficiency.

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For enclosed ground flares, the question of combustion efficiency is easily answered by installing and emissions monitor near the exit of the flare stack. For more on combustion efficiency, read the section on Smokeless Flaring.

Reliable Pilot and Ignition Reliable pilot operation under all wind and weather conditions is essential to the proper performance of a flare. The flare must be instantly available for emergency duty to prevent any possibility of a hazardous, or environmentally offensive, discharge to the atmosphere. Windshields and flame retainer are used to ensure continuous piloting under the most adverse conditions. Current flaring standards use flame-front ignition or spark ignition. Flame-front ignition is a remote system that shoots a ball of fire through a piping system to the pilot. Sparkignited pilots use the latest in technology to provide reliable ignition directly at the pilot. NAO uses a high-intensity ignitor located in the pilot tube to ignite the pilot gas. The spark-ignited pilot allows for faster response and less maintenance than flame-front ignition; the only drawback is that when maintenance is required on a spark-ignitor, the flare systems must be off-line. Flame-front generators may be serviced at any time because they are located away from the flare.

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Smokeless Flaring Today, smokeless flaring is required in most industrial applications onshore, and in many places, offshore regulations are tightening so that offshore flares also must be smokeless. Refineries are one of the areas where smokeless flaring is required. The most common method for achieving smokeless combustion is steam injection. Because of the availability of steam, most refineries use steam injection. There are some places, however, where steam isn’t available. If the flare is in a remote part of the refinery or it is in a gas plant where they don’t have steam, then you should consider other types of smokeless flares, including water-injection, multi-tip, and air-blower flares.

Jet Mix Flaring for Smokeless Operation The most cost effective way to achieve smokeless operation is with a Jet Mix Multi-Tip Flare. With the Jet Mix Tips, pressure is raised because the tips actually restrict some flow. This pressure is used to entrain combustion air as the gas exits the tip. The photographs show a comparison of flaring with and without the Jet Mix Tips. Without the tips, there was a pressure of about a pound or two. It was increased by the tips to about 15 to 20 psig. Usually for a Jet Mix Tip, you will need about 2 psig to assure good operation. For large turndowns, to maintain that minimum pressure you need Staged Flares. Essentially it is a main flare and a side flare—or as many as two or three side flares, all built on the same structure and the same flare tip. The different parts are activated as the flow increases. Normally this is by means of a very simple pressure switch and a staging valve. What we do is arrange all these valves in such a way that if you get an instrument failure or electrical failure, they will pop open. The flare might smoke at that time, but at least it will function. If that isn’t feasible, then we use in-line rupture discs or pressure-relief valves. Most of the time we use the fail-safe valves unless a customer wants it other way.

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Benefits of NAO Jet Mix Flares • No Assist Steam or Gas necessary • Best Turndown in the industry • Efficient Staging Controls

Steam Assist Flare NAO has variations on the steam assisted flare. The most basic is the NAO Fluidic Flare with Steam Ring (NFF-SR). It has a ring on the outside with a series of jets at the top. They pull in outside air and generate turbulence in mixing to make the flare smokeless. For large diameter tips and for some very smoky gases, we use a Ring and Center Steam Injection Flare (NFF-RC). The center injects steam with the hydrocarbon to insure complete combustion and smokeless operation. The center nozzle is especially important for a large diameter flare. The outer steam ring is able to inject steam and combustion air a distance of about 12 inches. Therefore, once we get up to a 24-inch flare, you begin to get a center core of gas that is not being mixed, which tends to produce some smoking. If the flare tip is more than 24inch in diameter, there is a need for a Center Steam Flare. Another advantage of a Center Steam Flare is its higher turndown with the ability to control the steam independently in both the center pipe and the outer ring. This provides higher turndown by operating each one in sequence. An example would be if we had a 150 psig steam. As we turn that down, about fourto-one, the four is squared to produce a 16-to-one pressure turndown—from 150 to about eight pounds! However, at eight pounds, the steam from the jets is so


Combustion Efficiency of Steam-Assisted Flares

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slow it won’t entrain any air or generate enough turbulence to do anything. With the option of reducing flow to the steam ring, you can increase the flow and pressure to the center steam and eliminate smoke at very low flows. To ensure that we have sufficient mixing and turbulence, we want to keep steam pressure at the tip above 10 psig. That isn’t practical if you have only one source of steam. But, with the Ring and Center Flare, you can control each one independently. When you reach the very low rates, you shut off the ring and just operate the center to provide the opportunity for additional turndown.

Advantages of NAO Steam-Assisted Flares 1. Efficient, Reliable Smokeless Combustion 2. Large Turndown 3. Maximum Air Entrainment with wide drilling pattern of steam tips 4. Small Steam Jets improve Turbulence and Reduce Steam Consumption 5. No Plugging of Steam Tips because steam jets drilled large enough to most particulate 6. More efficient than Water Injection 7. Lower Operating Expense than air assist or water injection 8. Lower Capital Cost than Enclosed Flares

The Fluidic Flare with a steam ring can be used vertically, horizontally or at any angle. Normally, flares are tipped horizontally or vertically. Very rarely is a flare tipped down and angled into a pit, but sometimes it is done. In pit installations, you have to prevent the flame from folding back over the flare tip and destroying or shortening the life of the flare—steam or water injection can help do this. Horizontal and angled flares are common offshore, though steam flares are not used offshore because steam is scarce, so airassisted or high-velocity Jet-Mix flares are recommended.

Water Injection Flare If steam is not available and Air-Assist or High-Pressure Flaring is not practical, you may choose the NAO Water

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Injection Flare. Offshore flares commonly use water injection because of the availability of seawater; it is pumped from below the platform and sprayed into the flare. Water injection flares are usually not very efficient. A typical steam flare consumes about a quarter of a pound to as much as a half pound of steam for each pound of hydrocarbon. A water spray flare could take as much a five pounds of water for each pound of hydrocarbon! That’s a lot of mass to pump. The key to the successful operation of a Water Spray Flare is very fine atomization of the water and getting it into the flame.

Benefits of NAO Water Injection Flares • Better Efficiency with very fine atomization • Fluidic Flare less susceptible to cross wind—this improves water injection performance

With water injection, it is very important to spread the water thoroughly into that flame. The biggest problem with water injection is cross wind. When the wind blows, the flame tends to blow out of the water-mixing region, then the unit starts to smoke and malfunction. With some applications, we have used something like a shower rack with many different nozzles for smokeless operation. Offshore, customers are not so concerned with smokeless operation. The main thing they are trying to do offshore is reduce the radiation from the flare; and water injection is an excellent way to accomplish that objective. It will reduce radiation by as much as 50%! Tipping the flame out away from the offshore platform with an angled Fluidic Flare also reduces radiation on the platform.

Air Assisted Flare If steam is not available and Jet Mix Flaring is not feasible, the next method of smokeless operation is an Air Blower Flare. Rather than use steam injection or high pressure to entrain air, you can push air into the gas stream using a blower. By providing adequate combustion air and

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additional turbulence, the flare combustion efficiency improves and smoke disappears. Typically, on an Air Blower Flare, it takes roughly five pounds of air for each pound of hydrocarbon. If you want to make one pound an hour smokeless, you need one standard cubic foot per minute of air. Hence, if you need 50,000 pounds an hour smokeless you need 50,000 standard cubic feet per minute of air. Another good rule of thumb is for each 1,000 pounds per hour smokeless, you need one horsepower of steam. , when you have an air flare there is no mixing of the air except at the very end of the flare tip. If there is any mixing inside, the combustible mixture will burn inside the flare and destroy it. Compressed Air is another type of Air Assist Flare; though it is commonly mentioned as a type of steam assist because it is operationally similar to steam injection. The compressed air entrains additional air and generates turbulent mixing of the air and the waste gas. The cooling effect of compressed air on the flare flame is less than with steam and, therefore, an additional 10% mass flow of air is required to match the effectiveness of steam. Due to the high cost of compression and the high pressure drop in the piping and injection system when using air, compressed air is rarely used on assist flares.

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Flare Systems NAO has manufactured complete flaring systems sin the 1970’s. These systems include the flare tips, the controls, and the flare structure. NAO Flare Systems include elevated flares, enclosed flares, ground flares, and pit flares.

Elevated Flare Typical Air Duct Sizes†

NAO makes a wide range of elevated flare stacks. The stack structures can be guyed, derrick, self-ing, or a combination of these. The stacks can include knock-out drums, water seals, ladders, platforms, and aircraft lights.

Capacity Pipe Size (MMscfd) (inch) 1 2 3 4 5 10 15 20 25 30 35 40 50 60 70 80 90 100

There are two important reasons for elevating a flare. One is to reduce the radiation at grade level to protect plant personnel. Plant personnel can safely work an 8-hour shift exposed to 400-500 Btu/ft2 of radiant heat (including solar). Plant personnel can safely evacuate an area during an emergency if radiation does not exceed 1,500 Btu/ft2. If radiation exceeds 1,500 Btu/ft2, personnel may receive burns before moving to a safe distance from the flare. Besides personal safety, flares should be elevated so that other equipment does not receive more than 3,000-5,000 Btu/ft2. The second reason for elevating a flare, and sometimes the most important, is to safely disperse toxic gases if the flare flame goes out. Though we design our flares for reliability during any weather condition, there is always a possibility of a pilot-gas failure or conditions that may snuff the pilots. If an emergency release occurs without an ignition source, lethal gases will be released to the atmosphere. If the flare is not properly elevated, these gases can collect in the plant.. Guyed stacks consist of elevated piping to the flare tip with wire-rope cables holding the piping erect. Guyed stacks are recommended where space is allowable because of their low-cost: As a rule of thumb, guy ed cable are at a 45° angle to the ground, so the system requires an area of land with a radius equal to the stack height. Guy cables must be maintained on a periodic basis (every 6 months) by greasing the cables and checking that they are properly tensioned (they stretch over time).

†

6 8 10 12 14 16 18 20 24 28 28 30 32 36 36 36 40 42

Low-pressure, boom-mounted air flare, 200 foot height


Self-ed stacks are generally the next option when choosing an elevated flare. Self-ed stacks rely on a wide base that narrows as it nears the flare tip. When a customer requires a water seal, knock-out drum, or both, we usually try to use these accessories as the self-ing base to save money. The third type of elevated flare is the derrick flare. These flares have a simple pipe as the flare stack with a derrick structure ing the it. The expense of purchasing and erecting the derrick structure that provides no benefit to the flaring system usually eliminates this type of flare structure from consideration. NAO has provided Articulated, or Self-Lowering, Derrick Flare Stacks. Articulated stacks have the sections of the stack ride up and down on a rail, so the entire stack can be raised and lowered from grade. This design is quite common in Europe where customers have multiple flares on a single derrick structure. The selflowering option allows customers to remove, repair, or replace a flare tip without disturbing the operation of other flares on the derrick.

Enclosed Flare In some applications, a customer may not have the land available for an elevated or a ground flare. Urban development commonly prevents companies from using open flares. In this case, an enclosed flare is a good solution. The Enclosed Ground Flare—or Populated Area Combustor (NPAC)—provides the closest control on the flare combustion process, with close temperature and air control. The emissions of the flare can be easily monitored from an attached platform since there is no thermal radiation hazard. If you were to look inside an Enclosed Flare you will see that there are a series of refractory blankets two-feet wide that line the entire chamber. These blankets are low density ceramic-fiber insulation and are sound absorbent. Because they are very low density they heat up very quickly and respond to changes in the flow stream very well. The density of NAO’s refractory lining is just over 5 pounds per cubic foot. Most other manufacturers use castable refractory very much like cement that is poured or gunited in place. The castable refractory is between 60 and 140

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NAO Guy ed Flare

NAO Self ed Flare


pounds per cubic foot. Because of its mass, it does not heat up quickly and it does not respond to changes in the flow stream. Also, the hard castable tends to reflect, not absorb, noise. Ceramic blanket, on the other hand, is very soft, so it actually absorbs the sound. Another benefit of the blanket is its flexibility. If a rain strikes and cools a small portion of the lining, the blanket can expand and contract, and it will not be destroyed. When rain hits a castable refractory, it will spall or crack.

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NAO Derrick Flare

Advantages of Enclosed Flares 1. No Assist Steam or Assist Gas needed for smokeless operation 2. Higher Combustion Efficiency—retained heat and residence time eliminate more of the harmful vapors 3. Combustion Air Control—enclosure eliminates effects of high cross winds 4. Low Noise with acoustical insulation 5. No Visible Flame 6. Low Radiation at grade 7. Easy Maintenance because nothing is elevated 8. Capability for Emissions Sampling

The NPAC operates using the chimney effect. A silo or chimney induces air by natural draft; the buoyancy of the hot combustion gases sucks in ambient air. Usually we also include a windshield or a fence around the outside so that wind variations do not disrupt the natural draft flow. The refractory lining inside the steel shell maintains the temperature inside the chamber, typically around 2,000 °F. The amount of heat emerging as hot gases is substantial at the top, but it is all air, carbon dioxide and water vapor. This unit operates at about 300% excess air, so the “neighborhood heat” is not excessive. (Carbon dioxide and water vapor radiate some heat, but they are only a very small percentage of the total flow, so the total heat radiated is very small.) In some operations, an enclosed flare operates in conjunction with an elevated flare. Daily and weekly lowflow rates are handled by the enclosed flare. When a major upset occurs, the elevated flare comes into service. On the left side of this illustration, there is a Knock Out Drum to

NAO Tripod Flare


remove any liquids and two Water Seals. One seal is to the left of the Ground Flare, the other is in the base of the elevated flare system. The water seal for the ground flare is very shallow, and the water seal on the elevated flare is very deep. For more information on water seals and knock-out drums, see the sections titled Flame Arresting Systems and Knock-Out Drums, respectively. For special applications, NAO has supplied Enclosed Flares for Production Ships and Roof Mounted Units. We once provide an enclosed flare for a municipal research facility where an open flame was not acceptable. It was necessary to eliminate radiation from the flame and to prevent light and noise from bothering the neighbors. The flare is rectangular, rather than circular, so it would blend-in more with other buildings and look like a cooling tower or an air conditioning unit. We also make very small units for landfills and sewage gas, and we have developed other small units for pilot plants, including Arco Research in Plano, Texas, and Union Carbide Institute in Charleston, West Virginia. The largest NPAC we have made is in a Polypropylene Plant in Taiwan. It is roughly 60 feet across and 100 feet tall, and it burns about 180,000 pounds per hour of propylene, which will burn very dirty and smoky if not handled properly. The biggest advantage of enclosed flares is that they don’t need steam or assist gas. Their smokeless operation is due to the large volume of entrained air and to the fact that it emerges from many tips. The flame is spread out so it gets plenty of combustion air. However, they can be expensive—the unit in Taiwan cost about two-million dollars plus another half-million dollars to install. This money is often recovered during the first two or three years of operation with the money saved on assist gas or steam.

Ground Flares If you have plenty of space, you can use an Iso-Fluidic Oxidizer (NIFO). Ground flares are generally staged. This allows the customer to use the pressure of the gas stream to ensure smokeless operation. Without staging, at low flow rates, the velocity of the gas will not be sufficient to entrain enough air for efficient combustion. If required, the NIFO

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can have an acoustical fence around it for very low noise attenuation. NAO makes enclosed ground flares such as the Vapor Control Unit (NVCU) and the Populated Area Combustor (NPAC). The open ground flare equivalent is called the Vapor Control Flare (NVCF). The enclosed unit is more popular today because there is a way of test emissions and prove that it works. With an open flare, there is no way to sample combustion efficiency. Our Vapor Control Units are used mostly for gasoline loading, either from trucks or barges.

Vapor Disposal Units • • • • • •

No Smoke No Visible Flame Low Noise Complete Destruction of vapors Quick Response to changes in flow conditions Safety Interlocks for smooth start-up/shut-down

For remote, open-space applications, such as production plants in deserts, NAO has designed the Mini Flare. The header piping is buried to prevent heat damage from the extremely high radiation. What you see are only the flare tips. In some applications, such as the desert, the ground is an insufficient heat shield, so we place a layer of gravel to act as a heat shield. The gravel is very coarse and irregular with a lot of air gaps. It acts like a closed-cell acoustic blanket to prevent heat from conducting through the soil to the flare header.

Pit Flares When flaring liquid-gas mixtures, pit flares are required. The flare fires horizontally into a shielded pit so that liquids can fall out and burn on the ground. Many times, customers have placed the flare tips through shielding walls that allow the flames to come up and destroy them. The flare must be shielded from flame impingement. They must be recessed into the wall without openings for the flame to enter. By packing the opening with a ceramic blanket, NAO provides

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flexibility between the flare and the wall without allowing the flame to get back into the flare. The pilots of a pit flare are usually remote. In other words, there is no venturi mounted at the bottom of the flare. Instead, there is up to 100 feet of piping (usually installed by the customer). All critical parts, including thermocouple, and venturi, are remote. Remote placement is to protect the equipment from flame lick and extend their life. Very rarely is a flare tipped down and angled into a pit, but sometimes it is done. In those installations, you have to prevent the flame from folding back over the flare tip and destroying or shortening the life of the flare. NAO has worked with customer to provide flare designs that reduce the likelihood of flame lick on down-fired flares.

Offshore Flares Because of the harsh environment and minimum space of offshore platform, NAO is one of the few flare manufacturers in the world that can supply flares to meet the specifications of offshore service. All of the flare designs used onshore are adaptable for use offshore. Because of constant high wind conditions offshore, as a minimum we extend the length of our conical windshields to reduce the damage caused by flame lick. Generally we supply flares with greater corrosion allowances and all-stainless-steel construction to extend their life. There are three types of flares for use with an offshore exploration or production drilling platform. Since steam is not available, other methods must be employed to assure smokeless flaring of the hydrocarbons. The tremendous problem of space confinement--personnel cannot run away--must also be considered in deg an efficient, reliable offshore flare. With an offshore platform, space is at a . The “packed-in” design, the proximity of work boats, and the difficulty (or impossibility) of personnel evacuation during an emergency, intensify the problems of thermal radiation associated with flaring for safety and environmental protection.

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When deg on offshore flare, the essential pre-requisites are: Experience, field-proven design, and a thorough, intimate knowledge of all factors involved in the mechanism of turbulent flow and momentum transfer for efficient air entrainment into gas masses.

Specialty Flares NAO has un-matched experience when it comes to deg portable flares. We were the first manufacturer to offer portable flares for rental applications. We have had four 8" x 80’ flare systems mounted on 40’ trailers in operation for over 10 years. These have been used throughout North America for emergency flare service and turnaround service on pipelines and at refineries, pharmaceutical plants, and other production plants. We have recently completed testing on a first-generation flare tip to burn low-Btu (50 Btu/ft3) waste gas without the addition of assist gas. Equipment using this new technology will pay for itself in less than one year.

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Flare Pilots NAO has many variations of the basic Flare Pilot, each with benefits for specific applications. NAO pilots come in two different sizes. A 2-inch-diameter pilot is the older design. It burns about 200 standard cubic feet per hour of natural gas at 10 psig. If you examine the illustration, you can see the thermocouple guide tube coming on the right side near the bottom. On the left side is the flame-front tube. The venturi and jet orifice are at the bottom. Our newer pilot is called an Energy Conservation Pilot. It is a 1¼-inchdiameter pilots that burns only 45 standard cubic feet per hour of natural gas at 10 psig.

Flame-Front Pilots The traditional flare pilot uses a 1-inch-diameter flame-front tube to send a ball of flame to ignite the pilot. These systems are common on flares around the world, particularly on elevated flares where the ease of maintenance of the flame front generator is recommended. Common problems of flame front pilots are water in the ignitor tube and changes of ignitor gas. Water will always collect in ignitor tubes. The ignitor combustion flame generates water vapor that, over time, will condense and collect at the low points of the ignitor tube. It is absolutely necessary for customers to provide drainage for their ignitor lines at the low points of the system. Often, customers rely on refinery gas to operate their pilots. The composition of this gas can vary from time to time, which means that the regulators of the flame front generator may not be correctly set. This requires that the flame front generator be manually adjusted when lighting the pilots.

Spark-Ignited Pilots The NAO High-Energy Spark-Ignited Pilot provides ultra-reliable ignition without compressed air or its associated moisture problems. The Spark-Ignited Pilot uses a 3,500-Watt spark to ignited the pilot gas while it is in the pilot tube. This eliminates the need for hundreds of feet of

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flame front ignitor piping and its associated problems. The spark ignitors have been successfully completed millions cycles in our in-house testing, and they have been field proven in ten years of installations. Because Spark-Ignited Pilots do not rely on compressed air for ignition, they rarely need manual adjustment for reliable pilot ignition—even as the composition of the refinery gas changes from day to day. This makes the spark pilot preferable to the flame-front pilot when deg automatic ignition/re-ignition systems.

Benefits of the NAO Spark-Ignited Pilot 1. No Compressed Air required 2. No Time Delay when lighting pilot 3. “Self-Cleaning” High-Intensity Spark blows off rust, water, ice, and dirt 4. No Water Drainage of ignitor line is required 5. No Re-adjustment required with variations in refinery gas 6. Low Pilot Gas Consumption and Operating Costs 7. Pilot Flame Stability under any weather condition

The only concern to have when selecting the Spark-Ignited Pilot is when deg elevated flare systems. If the spark exciter of the pilot should fail to work, the flare system must be shut down to service the elevated pilot. This maintenance concern can be corrected by specifying the Dual-Ignited Pilot.

Dual-Ignited Pilots Dual ignition pilots are becoming quite common today, especially in critical operations such as chemical plants. The dual-ignited pilots provide the benefits of quick, reliable pilot ignition with the spark ignitors and the ease-of-maintenance of the ground-level flame front system.

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Specialty Pilots The NAO standard is a straight pilot, but we also have our “Z” pilot, which are used as replacement pilots on brand X flares. To satisfy the need for stable pilots during nitrogen purges of flare systems, NAO now has the Air Eductor Pilot that uses a small flow of instrument air to draw pilot combustion air from the base of the pilot to the pilot nozzle; this prevents the nitrogen purge from snuffing the pilots. In some very special cases it’s not possible to use an inspirating type of pilot with a venturi. It could, for example, suck in sand with the air. Or, as in the arctic, snow and ice might plug up the air intake and freeze. For these situations, NAO has developed the Raw Gas Pilot with a little Jet Mix Tip inside the pilot shield. This is ideal where you have problems with plugging, such as from sand or freezing rains. The disadvantage of this type of pilot is that is it sucks up a lot of gas. It uses approximately 1,000 cubic feet per hour, but its perpetual flame is highly reliable. Some of these NAO units are used by BP in a pit in Alaska, and they have been burning since 1990 without any kind of interruption or change. The raw gas pilots can have flame front ignition or manual ignition with NAO portable ignitor, see the section on Pilots in the Burner section. At Sun Oil, Puerto Rico, they had a Brand X flare with four pilots, only one of which worked. They were concerned because if that one pilot went out, they would have to shut down the entire plant. Sun hired NAO to provide new pilots for the flare and to install them with the flare in operation. We used a very large mounting hook and put it on the windshield so we could attach the flare by using a crane, lifting it up, and attaching it to the Brand X flare tip. At the bottom of the pilot we put on two legs, so it would be kept away from the flare tip so that it wouldn’t get tangled into the existing pilots and piping; this worked very well. We had an individual, stainless-steel flexible gas line coming down for each one of the pilots. Tied to each hose was a thermocouple extension wire a 24-volt ignitor wire. We had an automatic ignitor at the flare base where we tied in with the thermocouple, electric and gas. For more information on how new pilots were installed on an operating flare, as for NAO Paper RP93-1.

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Pilot Ignition Systems NAO makes many different types of ignition systems, including those with air blowers, either electric or gasoline driven. One shows a small system, which was a combination ignitor and purge system, that we installed in the desert; the top is the ignitor; the bottom is the purge. We used solar cells for power and a little gasoline motor with a blower for combustion air. Our basic Flame Front Generator is the NAO Ignition (NIP). The one shown here has a three-way valve on the right and two three-way valves on the left for a total of three outlets. The number of valves needed is always one less than the number of pilots. The standard Automatic Ignitor comes with strainers on left side, pressure regulators and solenoid valves that automatically control the gas and air. There’s a by- around each of the solenoid valves, in case they malfunction. The other approach to using an ignition manifold is the a Flame Splitter. The Flame Splitter is a unit which has no three-way valves on the . The gas comes out of the ignition and up to the flare tip where it splits and ignites all the pilots, simultaneously. This works very well. NAO has tested a mile-long flame front ignitor pipe that lights all the pilots simultaneously. The benefit of the Flame Splitter is that it is very easy to use with an automatic ignition . With the three-way valves, you need a large, motorized valve to position each of the pilots sequentially. Large motorized valves are expensive and they are a problem because you have to coordinate the indexing and to the controller. We’ve done it often but the better approach is to use a flame splitter without valves. It is important to note that if an NAO pilot is already burning, nothing will happen to it—if you shoot up another ball of fire. This is because of the way we mount our flame front tube. If the flame front tube is not positioned properly, the “pop” of the ball of flame can snuff the pilot.

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Specialty Ignition Systems Many plant use “refinery gas” to supply their pilots. This refinery gas has varying levels of purity and can be all the cats-and-dogs in the gas system. One minute you might have all-hydrogen. Another minute, you might have allpropane, or something in between. This is very hard on the ignition because the gas/air ratio changes for different gases. With an Automatic Ignition , when the gas changes the settings are no longer correct. You have to go out and make manual changes. To compensate for this, NAO can custom engineer the automatic ignition to automatically adjust for different gases. If you don’t have compressed air, NAO has various other means of producing ignition. We have Inspirating Ignitors. We also have other electronic ignitors, such as the Offshore Sub-Sea Ignitor. If you tried to shoot a ball of fire underneath the sea inside a tube, you would get a lot of condensate—and a very quick failure! NAO uses a submarine cable which carries gas over to the ignitor. Then, an electrical signal produces the spark remotely. Inside that same cable may be thermocouple wires for automatic control of the ignition system. NAO was the first to develop the retractable pilot. The NAO Electronic “Elevator” System raises the pilot to ignite the waste stream, then lowers the pilot to protect it from the heat or to perform repairs. We also have Portable Spark Generators. These units use a 24-volt battery box to produce the spark. They also can be used for an inexpensive battery back-up in the event of a power failure. We can also supply battery back-up large enough to control the solenoid valves, temperature board, and spark ignitor of a fully-automatic spark-ignited pilot system. If you’re out in the field and don’t have any electric available, but do have compressed air, then you could use a Non-Electric Flare-Ignition System which uses a piezoelectric crystal. Or you can do the same basic thing when there is no compressed air or electric utility available with an inspirating ignitor.

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Liquid Knockout Drum If liquid condensate in the flare header is a problem, knockout drums, or disentrainment drums are necessary. Without a KO drum, liquid hydrocarbons will carryover to and burn on the flare tip. Since liquids burn hotter than the gases and since they burn directly on the metal, the metal degrades extremely quickly. A flare with liquid carryover can burn up in a matter of months. If a KO drum is used properly, this flare life can be extended to decades. If you were to look inside the drum you will see a baffle. The NAO drum is designed for a cyclone effect. The gas comes in tangentially so that it swirls around. Any liquid is thrown to the outside of the drum, falls down due to gravity, and is collected underneath the baffle. If you look carefully you will notice that the baffle does not extend out all the way to the wall. There is actually a gap to allow liquid accumulating on the walls to run down underneath the baffle. As the gas comes along and spins, it actually ducks down underneath that inner cylinder and then goes up the middle. That is a settling effect; when there is low flow that’s what actually knocks out the liquid. The center of the baffle is perforated, allowing the liquid to drop down. The reason for the baffle is to prevent surging and waves. If the device did not have the baffle, the liquid sitting at the bottom would act like the ocean in a hurricane. You would have waves and a lot of the liquid would be re-entrained—actually picked up by the gas flow. Information on flare accessories like Liquid Seals and Flame Arrestors can be found in the section titled Flame Arresting Equipment.

Knock-out Plot for Particulate Disentrainment


Flare Radiation The main factors affecting thermal radiation in a flare are: Flame temperature, flame emissivity, and flame tilt. A flame radiates heat from carbon particles, carbon dioxide, and water vapor. Nitrogen, though a large part of the combustion product volume, radiates very little heat due to its diatomic structure. Most of the radiation emitted from a flare, about 80%, comes from carbon particles. The energy radiated from a flame is proportional to the fourth power of the absolute temperature (≈T4) and is related inversely to the square of the distance from the flame (∝R2)—see the appendix for radiation calculations. Hence, for proper flare design, we have three objectives: Keep the flame as cool as possible, keep it free of unburned carbon particles, and keep it erect to maximize the effective height of the stack or boom.

Reducing Flare Radiation • Keep the Flame Cool • Eliminate Carbon Particles • Keep the Flame Erect

Flame emissivity—the ability of combustion products to radiate energy—is a property of the fuel being burned and of the fluid-dynamic pattern of the flaring system. The fluid-

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dynamic pattern of a flare is the turbulence in the flare flame generated by external energy sources. This turbulence is extremely beneficial. Turbulence increases combustion efficiency, decreases the emission of unburned gases, and substantially reduces the concentration of carbon particles in the flame. The end result is a substantial reduction in thermal radiation.

Exposure Limits NAO has conducted intensive research and test programs to determine flare performance and to measure actual radiation levels. Included in these programs are investigations of the actual skin-cooling effects of various ambient temperatures, different wind velocities, and different levels of relative humidity. By measuring actual values, we have shown that many established standards for maximum radiation exposure must play an important role in deg effective flares. These standard values indicate safe limits for radiation exposure. For instance, 1,500 Btu/hr·ft2 is generally taken as the maximum allowable radiation exposure at any time for personnel areas. If an emergency flare goes off, personnel will have about 30 seconds to evacuate an area before receiving painful burns on bare skin. For continuous operation, personnel can work in areas so long as radiation levels do not exceed 440 Btu/hr·ft2. It should be noted that these figures are very conservative. There is no provision for wind, ambient temperature, or clothing. The run-clear value of 1,500 Btu/hr·ft2, for example, is for bare skin. Many plants now have fire resistant clothing requirements and use 2,000 Btu/hr·ft2. The wind effect and ambient temperature can be even more significant than clothing. With a radiation intensity of 1,500 Btu/hr·ft2, 70 °F ambient temperature and no wind, a person will experience severe pain on bare skin within 30 seconds. With a radiation intensity of 3,000 Btu/hr·ft2 and a 30 °F, 30-mph wind, a person can continuously withstand the radiation exposure with any (or no) clothing. In cold climates, low solar radiation is generally combined with windy and frequently dry weather conditions, so people working around a flare will wear heavy clothing in order to be more comfortable. In hot climates, on the other hand,

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people will wear light clothing to be more comfortable with high solar radiation, high humidity, and little, if any, wind. We cannot design an efficient flare at low cost by using average values. Obviously, a design which is satisfactory for one set of parameters may be completely inadequate for another set of climate conditions. It is essential that flare engineering be handled by experienced people. They must have a wealth of background experience and not just rely upon a few outdated procedures, assumptions, and calculations.

Shielding Common sense must prevail when deg flare systems to reduce radiaiton exposure. The use of extremely long booms or other means of keeping the flame as far away from the offshore platform or personnel area must be restricted to practical mechanical desing applications. Shielding can effectively reduce the need for extra-long booms. Experience with water shields or water curtains has not been successful. Such shields can be valuable for fighting fires, but they cannot be made large enough to protect a relatively large area on an offshore platform. The corrosive effects of a continuous sea-water spray also rule out the use of water shields for normal day-to-day activities. Corrugated aluminum plates and screens shields are commonly used to shield the three levels of a derrick and to protect the sides of ladders and handrails on the flare side of a rig. This also serves as a noise barrier. Flare noise is discussed in the next section.

Radiation Pain Threshold Radiation Intensity Btu/hr•ft2 kW/m2 550 1.74 740 2.33 920 2.90 1,500 4.73 2,200 6.94 3,000 9.46 3,700 11.67 6,300 19.87

Time to pain seconds 60 40 30 16 9 6 4 2


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Flare Noise A big problem with a flare is the noise it generates. You have two sources of noise. One is the combustion noise, the low-frequency rumbling type. The other one is the highfrequency steam jet. Low frequency combustion noise is the sound of combustion and cannot be entirely eliminated. Combustion noise usually becomes a problem when a customer oversteams a flare. When too much steam is injected through a steam ring, a flame pulsation will occur—you will see the flame flare up every 1-2 seconds. To counter the effects of high-frequency steam noise with elevated flares, NAO has developed the Soft Mix Flare. This actually is an acoustically shrouded flare. It has a double-wall design with a mixing star at the very top. Steam is injected in the inner cylinder where is entrains air and pushes it out the top. This cylinder is shrouded, so the steam cannot be seen or heard. The steam-air mixture exits the inner cylinder through a mixing star at the flare tip where it mixes with the flare gas. Note: One caution with the Soft Mix Flare: If a turbulence level is too high, you will hear a lot of rumbling.

Recommended Design Flare Radiation Levels Excluding Solar Radiation Permissible Design Limit Btu/hr•ft2 kW/m2 5,000 15.77

3,000

9.46

2,000

6.31

1,500

4.73

500

1.58

Conditions Heat intensity on structures and in areas where operators are not likely to be performing duties and where shelter from radiant heat is available, for example, behind equipment. Permissible limit at design flare release at any location to which people have access, for example, at grade below the flare or on a service platform of a nearby tower. Exposure must be limited to a few seconds, sufficient for escape only. On towers or other elevated structures where rapid escape is not possible, ladders must be provided on provided on the side away from the flare, so the structure can provide some shielding when the design level is greater than 2,000 Btu/hr•ft2 (6.31 kW/m2). Heat intensity in areas where emergency actions lasting up to 1 minute may be required by personnel without shielding but with appropriate clothing. Heat intensity in areas where emergency actions lasting several minutes may be required by personnel without shielding but with appropriate clothing. Permissible limit at design flare release at any location where personnel are continuously exposed.

From API Recommend Practice 521


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Soft Mix Flares come with external steam rings for smokeless flaring at high rates—at that point, it’s usually an emergency—and the noise attenuation is not the primary problem. During normal operation, all of the required steam is enclosed. If a customer want to eliminate some of the noise on an existing flare, NAO can offer to replace their existing steam tips with the NAO Steam Dog tips. These are longer than our standard steam tips, and they inject the steam over a wider area of the combustion flame. This makes combustion more efficient (reducing low-frequency noise) and it increases the number of steam jets (reducing high-frequency noise). The Steam Dogs can be included on any new NAO Steam-Assisted Flare at a nominal cost.

Radiation Allowance for Ambient Temperature To be added

Radiation Allowance for Wind To be added

The most effective way to eliminate high-frequency steam noise is to eliminate the steam. This can be done by using an NAO Enclosed Ground Flare (the NVCU or NPAC). For more information, see the section on Enclosed Flares. Permissible Noise Exposure† Duration hours/day 8 6 4 3 2 1 ½ ¼ †

Sound Level dBA 90 92 95 97 100 105 110 115

From 29 CFR 1910.95

Typical Flare Noise Spectra


Flare Controls All flares require some kind of control system. The simplest are manual valves with manual push-buttons that require operations personal to physically monitor. With new regulations, however, these fully manual systems are rarely allowed. Most areas now require a monitor on the flare pilots to ensure that flame is always present.

Pilot Monitoring NAO recommends thermocouples to monitor pilot flames. We provide the option of complete pilot control packages with flares tip purchases and with pilot replacements on flare system refurbishments. On all NAO pilots with thermocouples, the thermocouples are enclosed in stainless steel guide tube that are enclosed inside the pilot tubes. This allows the pilot gas to cool the thermocouple and extend its life. In addition to the guide tube, NAO uses a thermowell in the pilot nozzle to prevent the pilot flame from directly impinging on the thermocouple. With the addition of this thermowell, we have extended thermocouple life in some applications from a few months to years and years. Besides thermocouples, NAO also has infrared pilot monitoring systems. These involve infrared detectors located at grade level that look for the heat of the pilot flame. Infrared monitors have one advantage over thermocouples in that these systems can be maintained while the flare is in operation; unless a customer has selected retractable thermocouples—an option on NAO pilots—the flare must be off-line to replace a damaged thermocouple. The problem with infrared monitors is that they cannot distinguish between pilot flames and flare flames. If the flare has two of three pilots out, the monitor may not detect the failure of the first two. This can have hazardous consequences if the third pilot fails as the plant dumps gas to the flare. With thermocouples, the status of each pilot is known individually. For more information on NAO Flare Pilots, see the section on Flare Pilots which follows.

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Steam Control NAO has several Automatic Control Systems for steam control. Generally, customers opt for advanced steam control technology to reduce the cost of operating their steam assisted flare. Sometimes, however, advanced steam control is necessary to prevent the noise associated with oversteaming the flare during low-flow operation. We have many different control systems today. The older system is a combination flow and radiation control system. It works by having a flow sensor in the flare header and radiation sensors at the top which provide a fine tuning. Today the trend is more towards optical control, which will be described later. That’s where you have an infrared pick up and it operates the entire process. That process is a little bit easier and simpler. The older control is ideal if you have just a very simple type of a flow, such as only propane or only butane. It’s also very good if you have a low Btu flare. A flare that will not burn by itself, one for which you have to add supplemental fuel. Under such conditions we can measure the flow of the waste gas coming along and then proportion in the amount of assist gas we need for complete combustion. The trend today, though, is towards optical systems. An optical sensor is mounted at the base of the flare to monitor and control the amount of steam going to the flare for smokeless operation. These controls look for molecular intermediates that form during combustion. If these intermediates increase, combustion efficiency is degrading, so steam flow is increased to keep combustion complete.

Other Controls Thermal Radiation Monitors, which are pyroheliometers or radiation-of-the-sun meters are used to monitor radiation levels of the flare. The are used as warnings, mostly offshore where knowing the level radiation is critical to personnel. These monitors are also used when highways or other roads nearby a flare. NAO also makes oxygen analyzers for flares. The Automatic Oxygen-Monitoring System continuously monitors oxygen levels in flare stacks and vents to assure

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safe flaring and venting of combustible gases. It calibrates itself every day. To reduce operations expenses, NAO has developed Energy-Conservation Control Systems to save energy by controlling the pilot and purge gases and turning them on only when necessary for flare relief. A popular conservation system is Purge Gas Control. This system will correct for temperature and flow and conserve purge gas. This is really not a critical type of service, but it is popular. NAO is now developing an Inert Gas Generator to use at the base of a flare stack to purge the flare stack using only instrument air. NAO has eliminated the need for control systems for pilots by developing the ultra-reliable conservation pilot. Most customers don’t favor automatic energy conservation systems because they have critical components. If the controller fails to operate, then they have to “dump the flare” because there’s no pilot ignition. By using Conservation Pilots, they have continuous, dependable pilots. That is why the control systems have fallen out of favor. Most people feel a lot safer by having a continuous running pilot.

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Flaring Applications NAO has decades of experience providing complete flaring packages to industry. This section discusses some typical flaring challenges that you might see. In addition to the sections that follow, keep in mind that NAO enjoys tackling new combustion challenges that our competition will not or cannot accept. We have the experience and the equipment to solve any feasible challenge a customer can present. NAO has truly been the worldwide leader when it comes to providing flares to industry. We were the first to develop flares for coke ovens and steel mills. Recently, we developed the first flare for the carbon black industry to operate without the necessity of assist gas.

Ammonia Terminals Next, let’s consider some of the different applications for flares. The photo to the right shows an ammonia terminal. Please note the small pipe, projecting above the tank. That’s actually the flare. Usually the flare is mounted on top of the access staircase going up the side of the tank. These flares are fairly small. They may be only 6, 8 or 10" in diameter. Operating at very low pressure, they resemble an NFF-CG flare. Ammonia burns well with only 6 or 7% unburned ash, but that doesn’t really matter because it’s an extremely rare event when one of these tanks will vent. The main reason for tank venting is failure of the ammonia refrigeration system, or loss of electric power which causes the refrigeration to fail. NAO uses a pressure switch on the top of the ammonia tank to activate the pilots. It is important to that the ignitor must have a battery backup, because when it is usually needed during a power failure. With our battery backup, the ignition system will work and the flare will burn the ammonia. With ammonia terminals, we usually don’t worry about complete combustion, because we get a fairly high efficiency rate.

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Landfill & Digester Flares With new regulations, landfills and wastewater treatment plants have been required to install vapor recovery systems or flares to destroy methane and other VOC’s that form as organic matter decomposes. The landfill, or digester, flare is enclosed by a shroud. Combustion occurs inside the shroud which hides part of the flame and insures a good stable incineration. There is a partially visible flame because this is not a fully enclosed flare. The flame may emerge two or three feet above the shroud. The gas burned in a landfill or digester flare is typically about half inert (nitrogen and carbon dioxide). Since the heating value is 400-500 Btu’s, it burns well. Sometimes, however, there are lower methane concentrations, and that’s why you need the shroud.

Steel Mills NAO has pioneered the use of smokeless flares for steel mills and coke ovens. During the late 1980’s, NAO did extensive testing at coke plants to develop the best design for their smokeless flaring of the dirty, low-heating-value gas. Our steam-assisted Fluidic Flare is considered by the EPA to be the Maximum Available Control Technology (MACT) for safe and reliable emergency flaring of cokeoven waste gas.

Portable Flares With over a decade of experience with portable flares, NAO has the expertise to provide reliable, long lasting flare systems that can be moved from site to site. These systems save customers money by allowing them to purchase one portable flare to use at many sites during turnarounds or during temporary flaring applications.

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Common Problems with Flare Systems Pilot does not light Wrong pilot gas pressure: Check the original design specifications for proper gas pressures. In general, NAO Conservation Pilots require 5-psig of propane and 10-psig of methane or natural gas, but this can change for special applications. Wet pilot gas: Condensate in the pilot gas collects in low points of the pilot gas line near the pilot and gets pushed along the along the pilot tube wall when the gas is turned on. This is more of a problem when using spark-ignited pilots. Plugged pilot tube, venturi, air adjustor, or pilot windshield: Corrosion, water, insects, and bats have plugged gas and air flow through pilots. Pilot gas filter is plugged: If the pilot gas filter plugs frequently, install a primary filter at grade that is convenient to replace. The filter on the pilot should remain in place. In spite of what operators may think, the filter will not plug nearly as quickly as the tiny orifice of modern (conservation) pilots.

Flame-front ignition failure Plugged ignitor tube: On start-up, if opening the compressed air causes back pressure on gas side, the ignitor and pilot gas tubes have been crossed or the ignitor tube is plugged. If the pressure gauges are slow to return to zero, the ignitor tube is partially blocked. No flame: The generator can fail due to improper air/gas mixture, wet gas or air, or power failure. Flame quenched: The flame front probably will not reach the pilot if there is condensate in ignitor tube, if an ignitor tube drain valve is open, if flex hose connections are used on the ignitor tube, if a strainer is in the ignitor tube, and if the ignitor tube is anything other than 1-inch pipe.

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Flame front blows out pilot flame: Ignitor tube smaller than 1-inch pipe or the ignitor tube length less than 100 feet. Also, if the air flow in the ignitor tube is too high, the mixture reaches stoichiometric proportions and detonates in the ignitor tube; this can damage light-gauge pilot windshields.

Spark ignition failure Power failure: Improper grounding of the 24-volt power supply or a broken wire prevents the ignition capacitor from charging. Water in exciter housing: Worn seals on the weatherproof housing can allow water to collect inside and short the ignition board. Spark ignitor failure: Excessive tar-like carbon build-up and long-term water immersion are the only known environments that have cause ignitor failure. Given time, though, the stainless steel spark ignitor can corrode. Radiation damage: Exceeding the design limits of the flare can damage the ignition board. If the problem is persistent, consider moving the spark-ignition components further from the pilot tip. Lightening strikes: The spark-ignitors have a small ignition board mounted on the pilot.

Pilots shut off automatically Pilot monitor failure: Pilot monitor does not detect flame due to monitor failure or low pilot temperature. Pilot gas solenoid valve failure: Most solenoid valves on pilot gas lines are normally closed. If power fails, the gas is shut off.

Pilot monitor failure UV/IR failure: UV/IR scanners cannot always distinguish between flare flame and pilot flame. If this occurs, move the

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monitors closer to flare and narrow their range of vision (i.e. don't target the entire flare tip from 3,000 feet, target a pilot from 500 feet). Thermocouple corrosion: Thermocouples placed in the flare flame can be exposed to excessive (H2S) corrosion attack. Thermocouples should be located below flare tip and out of the flare flame. Exposure to corrosion attack can be minimized or eliminated by using thermocouple wells and by locating thermocouple outside of flare flame. Thermocouple short: Water in Mineral Insulated sheath shorts thermocouple when corrosion destroys sheath or when epoxy potting head cracks due to vibration or during installation. This can be avoided by using thermocouple wells, by locating thermocouple outside of flare flame, and by using heavy-duty potting head at base of thermocouple.

Low pilot temperature Fuel gas composition not per design specifications: Using low heat value gas can lead to low pilot temperatures. Fuel gas pressure low: Low fuel pressure yields low gas flow. Pilot jet plugged or restricted: If the flame is small and lazy but pressures are correct, there is probably an obstruction in the line that is restricting gas flow. Pilot gas filter is plugged: If the pilot gas filter plugs frequently, install a primary filter at grade that is convenient to replace. The filter on the pilot should remain in place. In spite of what operators may think, the filter will not plug nearly as quickly as the tiny orifice of modern (conservation) pilots. Air adjustor restricted: The air adjustor needs to be opened or it is partially (or completely) blocked by corrosion. The pilot gas doesn't burn until it exits pilot windshield and mixes with additional air. The flame lifts off of the pilot nozzle and moves away from thermocouples. This can lead to pilot flame instability. Opening the air adjustor a little pulls the flame into the pilot and increases the temperature seen by the thermocouple.

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Pilot flame instability Low gas pressure: Check filters or strainers, provide a primary filter at grade level for ease of maintenance, if necessary. High gas pressure: The pilot gas velocity is so high that the flame lifts off of the pilot flame retainer. This makes the pilot susceptible to cross wind. Air adjuster improperly set: Inadequate air enters at venturi due to improper setting, corrosion, or accumulation of dirt. Corrosion of pilot windshield: Large holes in the pilot windshield short-circuit the windshield ability to block strong cross winds. Changing pilot gas composition: Variations in refinery gas composition result in different flame speeds. If the gas flow rate is constant, the pilot flame will move up and down inside the windshield. Snuffing during rain: Water can get into the air adjustor if it does not have a rainhood on the air adjuster. This rainhood is now standard on NAO pilots. Older systems may not have them. Inert gas purge: Using high nitrogen or other inert-gas purges on a flare system can starve the pilot of combustion air. This can be overcome by using eductor pilots that inspirate all of the required air ten feet or more from the flare tip.

Flare Smoking Plugged steam lines or steam tips: Particulate in dirty steam can collect at sharp turns in the steam line, of which there are many at the tip. Dirty steam comes from dirty water, from corrosion of the steam header piping, and from welding slag, gravel, and other junk in the header piping. When starting up a flare for the first time, make sure that the steam line is blown out prior to installing the tip.

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Low steam flow: Flow at less than design specifications can allow vapors to under steam tip of ring. This can be caused by the failure of steam control valves to open. Missing tips or cracked ring: Damaged steam rings entrain air inefficiently and can allow steam to miss flame zone. Poor turndown: Smoking of high-pressure Jet-Mix Flare at low flow. Jet-Mix Flares are designed to use the high pressure of the gas flow to entrain it own air for smokeless combustion. If design flow pressures change from original design specifications, a new tip or a staged system may be required.

Flare Noise Combustion noise: Some combustion noise is unavoidable when flaring. Efficient, stable combustion generates the least amount of noise. Pulsating, low-frequency noise: Caused by Oversteaming flare (better steam controls will provide proper amount of steam for a given gas flow rate) or excessive water-seal pressure drop (flow stops for a second at seal until pressure builds and a slug of vapor es). Continuous combustion rumble can be minimized by using NAO Steam-Dog steam tips. High-frequency steam noise: Some steam noise is unavoidable. If required, the steam injection for normal flare flow can be shrouded to minimize the continuous flare noise.

Flare Flow Restricted Molecular seal plugged: Mole seals collect loose refractory and water. These must be cleaned on a regular basis. Water seal plugged: In cold climates, the water freezes. The addition of glycol is a common solution. Flame arrestor plugged: Flame arrestors must be periodically removed from service and cleaned. Use a solvent or high-pressure steam or air to clean the arrestor.

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Knock-out drum plugged: Check for build-up of particulate or corrosion. Any trash in the flare header will eventually make its way into the knock-out drum.

Flashback in Flare Header Leakage in header piping: Flange leaks allow air to enter. Any flare gas that is lighter than air (mole weight = 29) will cause a slight negative pressure in the flare header as it rises by its own buoyancy. This is particularly dangerous at low flow conditions. Poor gas seal at tip: Allow for air ingress at low flow. Failure of water seal: Evaporation of water makes seal ineffective, the magnitude of this problem increases with flare gas temperature. Check level meters and the automatic fill equipment. Failure of flame arrestor: This is generally due to improper application or to a damaged grid. Flame arrestors must be periodically removed from service for inspection. If gas compositions change, the flame arrestor selection must be reviewed. A given flame arrestor does not work for all applications.

Cracked or Warped Flare Tip Low flow leads to flame lick: Use a solid conical windshield to protect flare body. Damage to the windshield is irrelevant compared to the problems associated with damage to the flare body. Liquid carry-over: Condensate in the waste gas is carried by the motion of the gas to the flare tip where it burns directly on the metal at a higher temperature than gas. Look for carbon build-up at tip (carbon residue in gas seal or tiger-stripes on outside of tip). Use a knock-out drum that functions properly to remove liquids from the gas stream.

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Cracked Steam Ring or Tips Lack of expansion ts: U-ts or bellows will allow for heat expansion and prevent cracks in the steam ring. On derrick flares where the flare stack moves relative to the structure and where the steam header is mounted to the structure, make sure the growth of the stack due to heat expansion does not pull the tip away from the steam line. Water hammer: Slugs of water in the steam strike the steam ring at high velocity. The water slams into the sudden restriction at the steam tip and puts large mechanical stresses on the steam ring. Installing good steam traps (bucket traps) to knock-out condensate should prevent this problem. Overheating: Operating a steam-assisted flare with no cooling steam then turning on steam can cause thermal stress and cracks in ring and tips.

Structural Damage to Stack Corrosion: Due to liquid carry-over (high H2S content). Sometimes liquids condense in the flare stack and collect inside the base; this quickly corrodes the metal and can cause the stack to lean; this also allows air to enter at the base of the flare and increase the potential for flashback. Loose guy wires: Cables should be inspected, tensioned, and greased every 6-12 months.

Staged Flare Problems Rupture disks: Rupture disks are prone to premature failure, particularly from downstream pressure. They must be replaced annually (this requires flare to be shut down). If this problem is persistent, switch to rupture pin valves (they are more expensive). Rupture pin valves are not prone to premature failure, they are not susceptible to back pressure, and they can be easily replaced without shutting down the flare.

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For Additional Reading “Combustion Tips,” Volume 1, Number 4, Safe Loading of Gasoline and other Flammables reviews applications for the Vapor Disposal Unit (NVDU), an enclosed ground flare. “Flare Technology Safety” is a general review of many flaring applications. “Flares: Design and Operation” is a six page review of flare design with calculations for thermal radiation. Included are schematics for refinery, pipeline, LPG storage, ammonia storage, and offshore flares. “Flaring for Gaseous Control in the Petroleum Industry,” NAO Paper #78-58.8, gives a brief introduction to smokeless flaring and describes in detail a fourmonth study done at NAO on 2-inch, 3-inch, and 6inch smokeless flares. “High Performance Offshore Flares” a presentation at the Fourth International Flare System Seminar discusses safety and engineering design criteria for offshore flares. “Solving Flare-Noise Problems” describes many good solutions for reducing decibel levels of smokeless flares. "Specifications for Flare System" provides a basis for developing a flare system specification for, particularly, a self-ed emergency flare. Ask for NAO Specification ELF-1.


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Thermal Oxidizers — Property of NAO Inc.

Thermal Oxidizers Thermal oxidation offers the safest, most effective and reliable solution to the problem of eliminating objectionable waste gases while complying with stringent regulations on air pollution control. The fuel for a thermal oxidizer may be the combustible waste product itself, or it may be augmented by a conventional fuel if the heating value of the waste stream is too low or too dilute. NAO designs, manufactures and services all combustion solution systems including Incinerators (today we use the words afterburner or thermal oxidizer–incinerator is a “dirty word”) and Vapor Control Units. NAO makes incinerators for gases, liquids, slurries and vapors–any kind of stream that can be pumped. A slurry, for example, would be pumped through one of our Atomizer Guns. For vapors, we use our patented Flame Arrestor Vapor Burner. If requested, we have thermal oxidizers with heat recovery like the NAO Liquid Incinerator. We recently supplied one to a pharmaceutical plant to generate 150-psi steam by burning spent alcohol. NAO’s portable thermal oxidizers include the VOCWagon,TM the VOCSkid,TM the VOCBox,TM and the large-capacity trailer-mounted PTOTM units available for lease, sale, or rental. These efficient fume incinerators are widely used in the oil, gas and petrochemical industries to control hazardous vapors and objectionable odors during tank clean-outs and other plant shutdowns. They are also used for soil remediation projects involving leaks or spills of gasoline, benzene, and other VOC’s.

Volatile Organic Compounds Volatile organic compounds (VOC’s) may be released to the atmosphere during routine processing in a refinery or in a chemical, petrochemical, or pharmaceutical manufacturing plant. More often, those dangerous VOC’s are vented to the atmosphere during emergency overloads, maintenance

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outages, equipment failures, liquid spills, or other accidental releases of carcinogenic, malodorous or highly flammable compounds. Because large clouds of hazardous vapors can be generated, the uncontrolled emission of VOC’s is detrimental to the environment on a global scale. It also creates serious safety problems in the immediate vicinity of a liquid spill or flammable gas cloud. Before the Clean Air Act was ed, many chemical and hydrocarbon vapors were routinely vented to the atmosphere. National regulations now limit VOC emissions from loading operations, including gasoline loading terminals for ships, barges, railroad tankcars and trucks, to less than 35 milligrams per liter of the loaded product. Some states are more stringent and demand better performance from new loading terminals before installation permits are granted. Other states are enacting new laws regarding emergency emissions of VOC’s caused by process upsets. There are also new regulations and pending legislation regarding the degassing of storage tanks. Florida now requires a total shutdown in the event of any process upset that created emissions in excess of 35 mg/ liter. In California, there are stringent controls on the degassing of storage tanks. Tank farm operators are being pressed to collect and oxidize the vapors released during periodic venting of their tanks. The Environmental Protection Agency (EPA) is enacting new regulations. Compliance with those new EPA regulations will be required before permits are issued by state and local Air Quality Control Boards.

Thermal Oxidation Systems For routine and intermittent venting of hazardous waste, a thermal oxidizer can be employed in conjunction with a vapor collection system. Permanently installed on-site, the thermal oxidation system will include burners, pumps, failsafe operating controls, and a water seal or flame arrestor on the waste-gas inlet. The fuel for a thermal oxidizer may be the combustible waste product itself, or it may be


Destruction Efficiency and Emission Profile†

augmented by a conventional fuel if the heating value of the waste product is too low. To insure complete incineration of hazardous or foul-smelling wastes, those wastes are subjected to temperatures between 1,400 °F and 1,800 °F for at least ½ second. The objectionable wastes are thus converted to innocuous ashes, carbon dioxide, and harmless water vapors. When halogenated compounds are incinerated, secondary pollutants are generated. For those applications, NAO’s thermal oxidizers incorporate integral scrubbers or particulate-collection subsystems to capture evolved hydrochloric acid, hydrofluoric acid, and other secondary pollutants. For permanent installations with optional gas scrubbers, the effluent gases are spray cooled in a quench chamber to remove non-combustible particulates and absorb the undesirable secondary pollutants. The particulates are

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Sizing Thermal Oxidizers Tflame + 460 1. ————— = GF Tgas + 460


filtered and the scrubbing liquor is pH adjusted and recycled. The exhaust gases, which are primarily carbon dioxide and water vapor, comply with the most stringent EPA and individual state regulations for air pollution.

2. FR x GF = FRact FRact 3. ——— = TOarea 40 ⎡ TOarea ⎤½ 4. ⎢———— ⎥ = TOID ⎣ 0.7854 ⎦ 5. TOID + 0.56 = TOOD 6. RT x 40 = TOSH FR FRact GF RT T flame Tgas TOarea TOID TOOD TOSH

Flow rate, scfm Flow rate, acfm Growth factor by temperature rise Residence time at Tflame, (½) seconds Oxidizer temperature, (1,600) °F Vapor temperature entering unit, °F Area of chamber, square feet Chamber inside diameter, feet Chamber outside diameter, feet Chamber height, feet

NAO Thermal Oxidizers • • • •

High-efficiency, low-NOx burners Capacities up to 100,000 scfm Combustion efficiencies 99+% standard Residence time of ½+ second at 1,400-1,800 °F standard • Field-proven low operational costs and low maintenance costs • Complete packaged systems with flame arrestors, water seals, and booster blowers Horizontal Thermal Oxidizer (NHTO) • Optional scrubbing and particulate collection systems • Optional waste heat recovery boiler or air preheater Vertical Thermal Oxidizer (NVTO) • Standard sizing reduces capital cost • Vertical design allows for natural draft firing–no air blower required–forced draft available

Portable Thermal Oxidizers By employing state-of-the-art designs for thermal oxidation and manufacturing self-contained, portable systems, NAO offers economic solutions to VOC problems where the cost of permanently installed equipment cannot be justified. These portable units, trademarked VOCWagon, VOCSkid, and NPTO provide solutions-to-go for serious liquid and air pollution problems. Designed for use in the event of a plant malfunction, equipment failure, or whenever an emission control system has been rendered inoperative due to a fire or mechanical or electrical shutdown, these units are designed to be set-up in a few hours with fully automatic controls to keep a plant on-line. These new, portable units have also been used for emergency spills, maintenance


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outages, and during the cleaning of pipelines, storage tanks, and process vessels. Available in three sizes to incinerate up to 39.950 cubic feet per minute of dangerous vapors, each trailer or skidmounted unit is completely self-contained. Positive flashback protection is assured by a unique flame arrestor head, a liquid seal, and automatic lockout controls.

Thermal Oxidizer Cost Estimate $40,000 $35,000 $30,000 Capital Cost $25,000 $80/hour

$20,000 Operating Cost

$15,000

$60/hour

$10,000

$40/hour

$5,000

$20/hour

1,000

3,000

5,000

7,000

9,000

Waste Vapor Flow Rate, scfm

11,000

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NAO Portable VOCSkid & VOCWagon • 1,200 scfm capacity • Proven 99+% combustion efficiency–complies with all federal, state, and local regulations • No visible flame, no smoke, very low noise • Packaged with complete controls and interlocks for automatic, un-attended operation • Easily transportable–on-line in a matter of hours • Flame arrestor burners handle any vapor composition • Adjustable natural-draft or forced-draft firing • Flame arrestors, water seals, booster blowers, and eductors are available • Factory technicians available for start-up and operations assistance

All of the portable units are ready for immediate, emergency service. They are available for short-term rental, for longterm lease, or, of course, for sale. Customers are welcome to inspect the portable rental fleet at any time. Equipment is stored and maintained at the home office in Philadelphia, Pennsylvania, and at the Environmental Research and Service Center northwest of Houston, Texas.


NAO Portable Thermal Oxidizer (NPTO) • 39,950 scfm capacity–only NAO has a temporary, portable unit with this capacity • Proven 99+% combustion efficiency–complies with all federal, state, and local regulations • No visible flame, no smoke, very low noise • Easily transportable–on-line in a matter of hours • Flame arrestor burners handle any vapor composition • Adjustable natural-draft firing • Flame arrestors, water seals, booster blowers, and eductors are available • Factory technicians available for start-up and operations assistance

NAO Thermal Oxidizers have been used: In plant turnarounds; for soil remediation and emergency clean-ups of leaks and spills; and to clean and maintain pipelines, storage tanks, process vessels, railcars, and tank farms.

Case In Point An NAO skid-mounted Thermal Oxidizer was used during the emergency clean-up of a million-gallon gasoline leak at a loading terminal on Long Island, New York. In addition to contaminating nearby streams, that massive leak formed a vast underground pool of gasoline. Volatile hydrocarbon vapors and carcinogenic benzene vapors from the underground pool threatened nearby neighbors. A standard pick-up truck towed a trailer with a VOCSkid oxidation unit to the site. Clean-up operations commenced after a relatively quick and easy hook-up. Since the hydrocarbon and benzene vapor stream was extremely volatile and rich enough to burn on its own, no assist gas was needed to incinerate that waste stream. The volatile vapors were sucked in by an explosion-proof, hermetically-sealed booster blower, which in this case handle 500 cubic feet per minute of the contaminated air/ vapor stream.

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Operating at approximately 1,800 °F, the skid-mounted unit provided a combustion efficiency of 99.9%, effectively destroying the rich fumes and preventing a potentially catastrophic explosion.

Applications EPA Testing & SuperFund Sites To determine the best method for controlling NOx levels from various waste streams, including strong ammonia streams, NAO has set-up portable thermal oxidizers for the EPA to test the effects of oxidation temperature, residence time, excess air, and recirculation. EPA tests concluded that NAO’s thermal oxidizer was “the best of four systems tested” before approving it for a SuperFund clean-up site in Rhode Island.

Chemical Plants Portable Thermal Oxidizers are used for controlling VOC’s from emergency upsets, liquid spills, off-spec products, storage tank blow-down, and process system turn-arounds.

Gas & Oil Storage and Transport Portable Thermal Oxidizers have been used for venting hydrocarbon and chemical storage tanks and for venting transport pipelines.

Pulp & Paper Mills Thermal oxidizers are used to destroy odoriferous sulfur compounds and non-condensable gases.


Common Problems with Thermal Oxidizers Failure on start-up Pilot failure: Gas pressure may be low, spark-ignitor may fail, or the pilot gas line or pilot tube may be plugged with corrosion or other particulate. Thermocouple failure: Thermocouples are directly exposed to combustion products and susceptible to chemical attack. If problem is persistent, consider exotic alloys for sheath material. Thermocouple wells will slow the response of the thermal oxidizer to changes in gas compostion, which should be avoided. Low assist gas pressure: The thermal oxidizer will not be able to achieve and maintain minimum oxidation temperatures without an adequate assist-gas supply. Low waste vapor pressure: UV scanner failure: The scanner may be out of alignment so that it does not see the pilot flame. The UV scanner can be blocked by corrosion, carbon particulate, or water condensate. Gas valves fail to open: After the thermal oxidizer reaches operating temperature, waste gas valves will be signaled to open on autmated systems. The valves may not be receiving this signal, or the valves may be stuck and failing to respond to the signal.

Flashback Burner manifold overheats: Flames may be curling under the burner tips and heating the piping over the auto-ignition temperature for the vapors. Combustible vapor mixtures require flame arrestors or water seals upstream of the burner. Flame arrestor failure: If gas compositions change, flame arrestors may also have to change. Arrestors must be periodically removed from service and inspected for

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damage. Cracked or shifted grids may compromise the arrestors effectiveness.

Temperature not maintained Too much combustion air: The oxidizer will not be able to maintain minimum temperatures if too much air enters the unit. Close natural-draft dampers or scale back the forceddraft blower. Not enough assist gas: Low assist-gas flow can be a result of un-open valves or undersized header piping that results in low pressure at the oxidizer. Change in waste vapor composition or flow rate: If changes are frequent and severe, the thermal oxidizer may not react fast enough to compensate. Properly designed equipment should minimize or eliminate this problem. Thermocouple failure: The equipment may be capable of reaching the set-point temperature, but failure to receive a signal from the thermocouple interpreted as low temperature.

Unit overheating Too much assist gas: Results when the modulating valve does not close or when gas pressure is too high. This is indicated by flames shooting out of the top of the thermal oxidizer. Continuous operation at excessive heat will damage the unit. Waste vapor flow rate too high: The flow rate of the combustible vapor mixture may exceed the design capacity of the thermal oxidizer. Change in waste vapor composition: If the heating value of the vapor increases more quickly than the response of the thermocouple and assist-gas modulating valve, the unit will quickly overheat.


Unit shuts down automatically Pilot failure: If the UV scanner does not prove the pilot flame on start-up, the unit will shut down. The UV scanner can be blocked by corrosion, carbon particulate, or water condensate. Low assist-gas pressure: Low assist-gas pressure will preclude low temperature in the oxidizer. The unit anticipate this and shuts down the waste gas flow. Low waste vapor pressure: This can be caused by booster-blower failure, undersized header piping, or restriction at the flame arrestor or water seal. High temperature set-point too high: If the high temperature set point is close the set-point operating temperature, the unit will quickly reach maximum temperature every time the waste vapor concentration or flow rate increases. Try to balance the operating set-point between the high and low set-points.

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For Additional Reading Capture Heat From Air-Pollution Control Systems is an NAO article that describes in technical detail the benefits of heat recovery systems for thermal oxidizers. Straitz, John F. III, “Flares & Thermal Oxidizers: Marine and Vapor Control” presents the combustion and oxidation techniques used to solve marine-terminal vapor-control and safety problems. Ask for NAO Report RP92-12. Straitz, John F. III, “Thermal incineration of VOC’s: Collection and control of volatile organic compounds” is a two-page report on the available systems for incinerating VOC’s. Ask for NAO Report RP94-2. For copies of these and other related technical papers, please mail or fax your inquiry to: Literature Department, NAO Inc., 1284 East Sedgley Avenue, Philadelphia PA 19134, Fax 215.743.3020.

Flame Arresting Equipment — Property of NAO Inc.

Flame Arresting Equipment There can be no margin for error with a Flame Arresting Equipment—Flame Arrestors, Detonation Arrestors, & Water Seals. It must work right the first time, and every time. When a subsonic deflagration or supersonic detonation reaches an arrestor, there is no opportunity to change variables. In the past 15 years, extensive full-scale deflagration and detonation tests at the Environmental Research & Service Center in Houston, Texas, and at our research facility in Philadelphia, Pennsylvania, supplemented by empirical calculations and tests at these and other NAO facilities, have enabled NAO to design and manufacture the widest range of state-of-the-art deflagration and detonation arrestors, including U. S. Coast Guard accepted and UL approved units. Every NAO flame arrestor is tested specifically for customer’s operating conditions prior to the sale of the arrestor. We do not sell an arrestor unless we are absolutely confident that it will quench a flame and prevent disaster.

Flame & Detonation Arrestors The flame arrestor is designed to stop a flame from ing through the gas source. The basic idea behind the flame arrestor design is that it must stop a gas/air mixture which has been ignited. A flame arrestor is placed between possible ignition sources and the gas supply. When the flame front reaches the flame arrestor grid, it is dispersed across the grid element and the heat is dissipated. If the flame arrestor is successful the flame is then quenched. If not, a catastrophe may occur.

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Arrestor Selection The flame arrestor selection process is important and sometimes time consuming. The selection of the correct flame arrestor will prevent a catastrophe from happening during usage.

Critical Flame Arrestor Design Information 1. 2. 3. 4. 5. 6. 7. 8.

Gas Composition Gas Temperature Gas Pressure Distance from all Ignition Sources Allowable Pressure Drop Maximum Gas Flow Rate Emergency Conditions Any Unusual Performance Characteristics

The arrestor selection process requires a minimum of information such as: Gas Composition, Gas Temperature, Gas Pressure, Distance from all Ignition Sources, Allowable Pressure Drop through the flame arrestor, Maximum Gas Flow Rate, and Any Other Information that makes the application out of the ordinary. Please note: If emergency conditions are known, they should be the basis of the arrestor design—i.e. at an emergency condition, the temperature is 595 °F, the pressure may rise to 25 psig, and a different gas composition may be present.

Flame Arrestor Type There are three types of arrestors. A Vent Arrestor, or End-of-Line Arrestor is located at the very end of a vapor pipe line. This arrestor vents gases to atmosphere. Some of the common sources of ignition may be static discharge, lightning, hazardous area or hazardous people.

NAO Vent Arrestor with rainhood

The next type of arrestor is the In-Line flame arrestor. This flame arrestor is generally not placed further then ten (10) pipe diameters from an ignition source. The last type of arrestor is the Detonation Arrestor. It covers in-line arrestors which cannot be placed within ten


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(10) pipe diameter of the ignition source. These arrestors may be situated in a pipeline or at the base of a tall flare system. Of these three types of arrestors, we manufacture a very wide range of flame arrestor configurations. Standard arrestors come flanged, threaded, and plain for placement between flanges. Often, customers avoid flanges to reduce costs; on large units, flanges can double the cost of an arrestor.

In-line Flame Arrestor

Arrestors come in any size over ¾-inch diameter. Large custom units have been built up to 12 feet in diameter. Any of our arrestors can be custom engineered to satisfy any piping requirements. Some In-line arrestors actually have a water spray to wash off the grids. Vent arrestors often have a “Chinese hat” or flapper hood on it to keep rain and snow off of the grid. Usually this is put on a tank as a vent, so the tank can breath and emit the various fumes.

In-line Flame Arrestor with expanded grid for low pressure drop

If pressure drop is a main concern, we can make an expansion arrestor. For instance, you might have a 4 inch pipe with a 6-inch or 8-inch flame arrestor grid. Using the wider grid element, we can often reduce pressure drop to 12 inches of water column.

Flame & Detonation Arrestor Approval NAO has UL 525 approval for the Vent Arrestor. NAO also has United States Coast Guard acceptance for the detonation arrestor. These approval processes help insure that the arrestor is tested and operates efficiently with the worst possible cases that can be present in an application. However, we have tested UL and FM approved arrestors manufactured by our competition that have failed our testing program. We do not sell any safety device that does not meet and sur industry standards or our standards. Large capacity in-line Flame Arrestor

Water Seals Last, but not least, is the Liquid Seal. We make a wide range of sizes of these units, from 1 foot in diameter and 3 feet high to units that are 40-feet long and 10-feet in

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diameter—these are for very-large flare loads. With a water seal, the gas comes in through a bubble plate that breaks it up into many small bubbles. You can see distinct or separate bubbles rising through the liquid. If one of the bubbles catches fire and explodes, it can’t get to the next one, so the flame is quenched. NAO did a lot of testing on water seals for a nuclear facility, called Three Mile Island in the early 1980’s. There they had a mixture of hydrogen and oxygen, which is a very fast burning gas. The flame speed—15,000 mph—was a major concern. We developed standards for bubble patterns and bubble diameters to effectively quench this flame. We then designed a special unit that had twice the area of a standard seal because the gas mixture exploded so violently that, in a standard seal, one bubble would have ignited the next.

NAO Water Seal

For staged flare flows, NAO makes a Dual Stage Horizontal Water Seal. It is actually a drum, divided into two different parts. By dual stage we mean that there are different levels of water in it. One is shallow and one is deep. As flow and pressure increase, the second stage comes on automatically. Many times, water seals are used as the base of a selfing flare because they serve as an economical foundation and structure. Separate drums can be expensive because you have to have separate foundations, s, and piping for them. If required, knock-out drums are also incorporated with water seals to reduce the cost of the equipment.

NAO Research & Development NAO performs testing for various applications and for specific customer requests. NAO has two testing facilities. One facility is located in Philadelphia, Pennsylvania, and the other is in Plantersville, Texas, northwest of Houston. The smaller and quieter tests are performed at the Philadelphia

NAO Disentrainment Drum with integrated Water Seal


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facility. The larger and louder tests are conducted at the Plantersville facility. Between the two facilities, we have the capability for full-scale testing of any flame or detonation arrestor.

Common Problems with Flame Arrestors Flame age Improper arrestor location: Flame arrestors should be located no more than 5-10 pipe diameters from the source of ignition. Mis-application of arrestor: Arrestors should be designed for the most dangerous gas in a vapor mixture at the worst possible conditions—highest temperature, highest pressure. Continuous burning: Flame arrestors should have thermocouples to indicate when continuous burning is taking place on the grid. Without flame detection, the temperature of the grid can quickly exceed the auto-ignition temperature of the vapor, particularly at low flow conditions. High vapor temperature: The higher the temperature of the waste vapor, the more dangerous the condition. Changing gas compositions: Arrestors should be designed for the most dangerous gas in a vapor mixture at the worst possible conditions—highest temperature, highest pressure. Changing gas pressure: High pressure is difficult to arrest. The highest possible pressure must be specified when selecting an arrestor. Cracked or shifting grid: Arrestors should be periodically removed from service and inspected for damage. Arrestors must be inspected after a known flashback to determine if the shock of the explosion shifted or cracked the grid.

NAO 18" Flame Arrestor Test

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High Pressure Drop Plugging of grid: The pressure drop across the grid should be monitored. Over time the pressure loss will increase as the arrestor begins to plug from particulate in the vapor stream. If the problem is persistent, two arrestors should be used in parallel so that one can be removed with the vapor line in service, or the customer should consider using a water wash to clean the grid while it is in service. Grid size too small: The smaller the grid, the safer the design; but the smaller the grid, the higher the pressur drop. If necessary, surface area of the grid can be increased to reduce the pressure drop. Not enough surface area of grid: An expanded arrestor design—for example, using a 4-inch grid on a 2-inch line— can provide safety and a low pressure drop.

Plugging of Grid Matting of dirt on surface: Particulate in the vapor stream collect in the small openings of the flame arrestor grid. Clean the grid by using solvent or high-pressure steam or air. Never pick at or drill out the debri. Freezing of condensate in grid: The flame arrestor grid acts as a perfect condenser. If ambient temperature is below freezing, condensate in the vapor stream will freeze and plug the grid. Heat tracing or a glycol spray can prevent freezing of the grid element.

Mis-Application of Arrestor Location of arrestor: The further from the ignition source, the more difficult it is to arrest the flame. As rule of thumb, if the arrestor is located more than 5-10 pipe diameters from ignition source or if it is located at entrance to furnace or heater, a detonation arrestor may be required (depending on gas composition). No universal arrestors: Customer must specify all possible gases that may be present in an application. The arrestor must be designed for the most dangerous gas in the mixture.


If the gas composition changes, the arrestor design must be reviewed. Group A & B gases: Group A & B gases are the most difficult to arrest. Group A gases include any mixture containing acetylen. Group B gases include any mixture containing gases like hydrogen, ethylene oxide, and butadiene†. Group C & D gases: Group C & D gases are easier to arrest. Group C gases include any mixture containing ethylene or carbon monoxide. Group D gases include any mixture containing gases like methane, propane, and butadiene†. †

Butadiene behaves as Group B gas at some temperatures and pressures, and as Group D at others. All gases can produce intermediate products during an explosion. These intermediate products can be more dangerous than the original gases.

9-7

9-8


For Additional Reading Mendoza, Smolensky, & Straitz, “Flame Arrestors: Selection, Design and Testing” is an eight page report on NAO criteria used when deg and testing flame arrestors and water seals. Ask for NAO Report RP93-7. Straitz, John F. III, “Arrestors Guard Against Explosions” is a two page article describing the essential criteria of flame and detonation arrestors. Ask for NAO Report RP94-5. For copies of these and other related technical papers, please mail or fax your inquiry to: Literature Department, NAO Inc., 1284 East Sedgley Avenue, Philadelphia PA 19134, Fax 215.743.3020.

Vents — Property of NAO Inc.

Vents Vents are used on-shore and off-shore to release combustible and inert vapors to atmosphere. Two critical factors must be considered when deg a vent system: The vent must prevent air from entering the line be vented, and the vent must disperse gases to prevent dangerous vapor clouds from forming around equipment and personnel. When storing fuels under atmospheric pressure, customers must leave an opening in a storage tank to relieve pressure. This can be hazardous, however. Lightening or static discharge can ignite vapors that mix with air near the tank. If air gets into the tank, explosions and tremendous fires can result. Depending on the nature of the gas being vented, there are three types of vent tips: Gas seals, vent arrestors, and JetMix™ vents.

Gas Seals There are two types of gas-seal vents. The first, and the most popular, is the Fluidic Vent. The Fluidic Vent is an application of NAO's patented Fluidic Seal. The second type of gas-seal vent is the molecular seal. Both protect vent lines by preventing air entry. The Fluidic Vent has a number of advantages over the molecular seal. At a given flow rate, the Fluidic Vent is more effective at diffusing air than the molecular seal. For the Fluidic Vent, the pressure drop for reverse flow through the vent is four (4) times greater than normal flow of the same rate. For a molecular seal, the pressure drop is the same for normal and reverse flow. It is more difficult for air to move in the reverse direction with the Fluidic Vent than with the molecular seal. The Fluidic Vent can be installed in any direction. The nomoving-parts venturi design of the Fluidic vent do not limit it to vertical applications. The molecular seal is a gravity seal.

10-1

10-2


If installed at an angle or horizontally, it ceases to function. The Fluidic Vent does not depend on gravity action, so it can be used effectively in horizontal angled applications. In addition to better performance, the Fluidic Vent also requires less maintenance than the molecular seal. The Fluidic Vent is manufactured from high-temperature stainless steel and it does not collect condensate. The molecular seal is usually fabricated from carbon steel, which corrodes, and it collects condensate; this condensate accelerates corrosion and restricts flow through the seal. In some locations, the molecular seal must be heat traced to prevent freezing of the condensate. Another advantage of the Fluidic Vent is its low profile and light weight. The molecular seal is, typically, twenty times as heavy as the equivalent Fluidic Vent and two times its diameter; this adds to the structural load of the vent and requires larger structures.

Advantages of the Fluidic Vent • Simple, straight-path, wall-less venturi flow path for waste gas • No plugging • Light-weight • Low profile reduces wind loading • Works in any direction—vertically, horizontally, and any angle in between • No moving parts • No drainage or corrosion problems

To prevent static electricity from discharging in the vent pipe and igniting vapors, we offer the option of electrostatic rings on the vent. You must be very careful with high gas velocities or if you have any liquid particles which cause a static electric buildup that could cause ignition. With the static rings, there are no sharp edges, and this insures no buildup in static electricity. If a vent does ignite, NAO makes various Automatic Fire Suppression Systems that use either dry chemical, CO2, or Halon to extinguish a fire. If you want to extinguish a fire on a very large vent, it is often cost effective to use a Jet Mix


Fire Suppression System. This sucks in a lot of air with the combustible gas so that it will just barely burn. In this case, it doesn’t take much dry chemical or CO2 to snuff out a fire.

Flame Arrestor Vents When venting vapors at low flow rates, dispersion will be very low when the wind velocity is low. The resulting vapors will be a combustion hazard. To eliminate the possibility of flashback under these conditions, flame arrestors designed to quench the flame can be used on an end-of-line vent. Flame arrestor vents are often used as pressure relief vents on storage tanks where vapor volumes change as atmospheric temperature rises and falls. Often, these vents come with rainhoods to prevent the collection of condensate in the vent line. For more information on flame arrestor vents, see the chapter on Flame Arresting Systems.

Jet-Mix Vents Jet-Mix Vents are used where toxic and highly combustible vapors are vented. Jet-Mix Vents allow for very good dispersion of the gases by spreading the vent tip over a wider area and by increasing the velocity of the gases being vented.

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Property of NAO Inc.

Appendix A-1

Unit Conversion Basic and Derived Standard Units Length Mass Time Temperature Force Pressure Energy, work Power

U.S. Customary Unit Symbol Formula foot ft * slug slug lbf·s2/ft second s * Rankine R * pound

lbf

* lbf/ft2 ft·lbf ft·lbf/s

Unit meter kilogram second Kelvin

SI Symbol m kg s K

Formula * * * *

Newton Pascal Joule Watt

N Pa J W

kg·m/s2 N/m2 N·m J/s

*base unit

Unit Prefixes Factor 10-18 10-15 10-12 10-9 10-6 10-3 10-2 10-1

Prefix atto femto pico nano micro milli centi deci

Symbol a f p n µ m c d

Factor 101 102 103 106 109 1012 1015 1018

Prefix deka hecto kilo mega giga tera peta exa

inches 1 12 39 370 39.37 63 360 36

feet 0.0833 1 3 281 3.281 5 280 3

km meter mile* 2.540E-5 0.02540 1.578E-5 3.048E-4 0.3048 1.894E-4 1 1 000 0.6214 0.001000 1 6.214E-4 1.609 1 609 1 9.144E-4 0.9144 5.682E-4

Symbol da h k M G T P E

Length 1 inch 1 foot 1 kilometer 1 meter 1 mile 1 yard

*1 mile = 0.8688 nautical mile 1 fathom = 6 feet 1 furlong = 10 chains = 40 rods = 220 yards

yard 0.0278 0.3333 1 094 1.0936 1 760 1


Appendix A-2

Unit Conversion Area 1 acre 1 cm2 1 ft2 1 hectare 1 in2 1 km2 1 mile2 1 m2

acre* 1 1.941E-8 2.296E-5 2.471 1.594E-7 247.1 640.0 2.471E-4

cm2 4.047E7 1 929.0 1.000E8 6.452 1.00E10 2.590E10 10 000

ft2 43 560 0.001076 1 107 639 0.006944 1.076E7 2.788E7 10.76

hectare 0.4047 1.000E-8 9.290E-6 1 6.452E-8 100.0 259.0 1.000E-4

in2 km2 mile2 6.273E6 0.004047 0.001563 0.1550 1.000E-10 3.861E-11 144.0 9.290E-8 3.587E-8 1.550E7 0.01000 0.003861 1 6.452E-10 2.491E-10 1.550E9 1 0.3861 4.014E9 2.590 1 1 550 1.000E-6 3.861E-7

m2 4 047 1.000E-4 0.09290 10 000 6.452E-4 1.000E6 2.590E6 1

1 acre = 4 roods = 160 square rods = 4 840 square yards

Volume inches3 feet3 meter3 liter fluid oz US gallon UK gallon 1 inch3 1 5.787E-4 1.639E-5 0.0164 0.5543 0.004329 0.003604 1 foot3 1 728 1 0.02832 28.32 0.001044 7.481 6.229 1 meter3 61 024 35.32 1 1,000 33 810 264.2 220.0 1 liter 61.024 5.787E-4 0.001000 1 33.81 0.2642 0.2200 1 fluid ounce 1.804 957.9 2.958E-5 0.02957 1 0.007812 0.006505 1 US gallon 231.0 0.1337 0.003785 3.785 128.0 1 0.8327 1 UK gallon 277.4 0.1605 0.004546 4.546 153.7 1.201 1 1 US barrel 9 702 5.615 0.1590 159.0 5 376 42.00 34.97 1 acre-foot 7.527E7 43 560 1 233.5 1.233E6 4.171E7 325 85 2.713E5 1 US pint 28.88 0.01671 4.732E-4 0.4732 16.00 0.1250 0.1041 1 US quart 57.75 0.03342 9.464E-4 0.9464 32.00 0.2500 0.2082

US barrel 1.031E-4 0.1781 6.290 0.006290 1.860E-4 0.02381 0.02859 1 7 758 0.002976 0.005852

Mass 1 gram 1 kilogram 1 ounce 1 pound 1 short ton 1 long ton 1 metric ton 1 slug 1 dram

g 1 1 000 28.35 453.6 9.07E5 1.02E6 1.00E6 14 594 1.772

1 slug = 1 lbf·s2/ft

kg 0.001 1 0.02835 0.4536 907.2 1 016 1 000 14.59 0.00177

oz lb m short ton 0.03527 0.002205 11.02E-7 35.27 2.2046 11.02E-4 1 0.0625 3.125E-5 16.00 1 0.00050 32 000 2 000 1 35 840 2 240 1.120 35 274 2 205 1.102 514.8 32.17 0.01609 0.06250 0.003906 1.953E-6

long ton metric ton slug 9.842E-7 10.0E-7 6.852E--5 9.842E-4 10.0E-4 0.06852 2.790E-5 2.835E-5 0.001943 4.464E-4 4.536E-4 0.03108 0.8929 0.9072 62.16 1 1.0160 69.62 0.9842 1 68.52 0.01436 0.01459 1 1.744E-6 1.772E-6 1.214E-4


Appendix A-3

Unit Conversion Force 1 dyn 1 kip 1 lbf 1 poundal 1N

dyn* 1 4.448E8 444 822 13 826 100 000

kip lbf poundal** N 2.248E-9 2.248E-6 7.233E-5 1.000E-5 1 1 000 32 174 4 448 0.001000 1 32.174 4.448 3.108E-5 0.03108 1 0.1383 2.248E-4 0.2248 7.233 1

*1 dyn = g·cm/s2 **1 poundal = 1 lbm·ft/s2

Pressure 1 atm 1 bar 1 kg/cm2 1 kPa 1 inch Hg 1 mm Hg 1 inch H20 1 N/m2 1 psi (lbf/in2) 1 dyn/cm2 1 micron 1 mm H20 1 osi 1 torr

atm 1 0.9870 0.9678 0.009869 0.03342 0.001316 0.002456 9.869E-6 0.06805 9.869E-7 1.32E-6 9.668E-5 0.00425 0.001316

kg/cm2 kPa* inchHg** mmHg** inchH20*** lbf/in2 1.033 101.3 29.92 760.0 407.2 14.70 1.020 100.0 29.53 750.1 401.9 14.50 1 98.07 28.96 735.6 393.1 14.22 0.01020 1 0.2953 7.501 4.019 0.1450 0.03453 3.386 1 25.40 13.61 0.4911 0.001360 1.333E-5 0.03937 1 0.5358 0.01934 0.002537 0.2488 0.07347 1.866 1 0.03609 101 971 0.0010 2.953E-4 0.007501 0.004019 1.450E-4 0.07031 6.895 2.036 51.71 27.71 1 1.020E-6 1.000E-4 7.501-4 7.501E-4 4.019E-4 1.450E-5 3.94E-5 1.000E-3 1.95E-5 9.796E-5 9.989E-5 0.009796 0.002893 0.07347 0.03937 0.001421 0.00431 0.004394 0.430 0.1272 3.233 1.732 0.0625 0.001333 0.001360 1.333E-5 0.03937 1 0.5358 0.01934

bar 1.013 1 0.9807 0.01000 0.03386 0.001333 0.002488 100 000 0.06895 1.000E-6

*1 Pa = 1 N/m2 **32°F, 0°C, 1 mmHg = 1 torr ***60°F, 15.6°C

Velocity 1 ft/min 1 ft/s 1 inch/s 1 km/hr 1 knot 1 m/s 1 mile/hr 1 mile/s

ft/min 1 60.00 5.000 54.68 101.3 196.9 88.00 316 800

ft/s 0.01667 1 0.0833 0.9113 1.688 3.281 1.467 5 280

in/s 0.2000 12 1 10.94 20.25 31 557 17.60 63 360

km/hr knot m/s 0.01829 0.009874 0.005080 1.097 0.5925 0.3048 0.0914 0.0494 0.0254 1 0.540 0.2778 1.852 1 0.5144 3.600 1.944 1 1.609 0.869 0.4470 5 793 3 128 1 609

mile/hr 0.01136 0.6818 0.0568 0.6214 1.151 2.237 1 3 600

mile/s 3.157E-6 1.89E-4 1.58E-5 1.73E-4 3.20E-4 6.21E-4 2.78E-4 1


Appendix A-4

Unit Conversion Acceleration free fall 1 ft/min2 1 ft/s2 1 km/hr2 1 m/s2 1 mile/hr2

ft/min2 ft/s2 km/hr2 m/s2 mile/hr2 115 027 32.17 127 094 9.807 6.094E-6 1 2.778E-4 1.097 8.467E-5 0.6818 3 600 1 3 950 0.3048 2 455 9.113E-4 2.532E-7 1 7.716E-5 0.6214 11 811 3.281 12 960 1 8 053 1.467 4.074E-4 1.609 1.242E-4 1

Volume Flow Rate ft3/min 1 ft3/min 1 1 ft3/hr 0.0167 1 US-gal/min 0.1337 1 l/min 0.0353 1 m3/s 2 118.9

ft3/hr US-gal/min l/min 60 7.481 28.32 1 0.1247 0.472 8.021 1 3.785 2.119 0.2642 1 1.27E5 15 850 6.0E4

m3/s 4.72E-4 7.87E-6 6.31E-5 1.67E-5 1

Mass Flow Rate 1 g/s 1 kg/hr 1 lbm/hr 1 lbm/min 1 ton(metric)/day 1 ton(short)/day

g/s 1 0.2778 0.1260 7.560 11.57 10.50

kg/hr 3.600 1 0.4536 27.22 41.67 37.80

lbm/hr 7.937 2.205 1 60.00 91.86 83.33

lbm/min ton(metric)/day ton(short)/day 0.1323 0.08640 0.09524 0.03674 0.02400 0.02646 0.01667 0.01089 0.01200 1 0.6532 0.7200 1.531 1 1.102 1.389 0.9072 1

Energy Btu 1 Btu 1 1 erg 9.478E-11 1 ft·lbf 0.001285 1 hp·hr 2 544 1 kcal 3.968 1 kJ 0.9478 1 kW·hr 3 412 1 cooling-ton·hr 12 000

erg* 1.055E10 1 1.356E7 2.685E13 4.187E10 1.000E10 3.600E13

*1 erg = 1 dyn·cm **1 kJ = 1 000 W·s = 1 000 N·m

ft·lbf 778.2 7.376E-8 1 1.980E6 3 088 737.6 2.655E6

hp·hr kcal kJ** kW·hr 3.930E-4 0.2521 1.055 2.931E-4 3.725E-14 2.388E-11 1.000E-10 2.778E-14 5.051E-7 0.3238 0.001356 3.766E-7 1 641.2 2 685 0.7457 0.001560 1 4.187 0.001163 3.725E-4 0.2388 1 2.778E-4 1.341 859.8 3 600 1


Appendix A-5

Unit Conversion Specific Energy 1 Btu/lbm 1 cal/g 1 kW·hr/kg 1 kJ/kg

Btu/lbm 1 1.800 1 548 0.4299

cal/g 0.5556 1 859.8 0.2308

kW·hr/kg 6.461E-4 0.001163 1 2.778E-4

kcal/m3 8.904 1 0.2388

kJ/m3 37.26 4.187 1

kJ/kg* 2.326 4.187 3 600 1

1 kJ/kg = kW·s/kg

Energy Density 1 Btu/ft3 1 kcal/m3 1 kJ/m3

Btu/ft3 1 0.1123 0.02684

Heat Release — Power 1 Btu/hr 1 ft·lbf/min 1 hp 1 kcal/hr 1 kJ/hr 1 kW

Btu/hr ft·lbf/min 1 12.97 0.07710 1 2 544 33 000 3.968 51.47 0.9478 12.29 3 412 44 253

hp kcal/hr 3.930E-4 0.2520 3.030E-5 0.01943 1 641.2 0.001560 1 3.725E-4 0.2388 1.341 859.8

kJ/hr 1.055 0.08135 2 685 4.187 1 3 600

kW* 2.931E-4 2.260E-5 0 7457 0.001163 2.778E-4 1

*1 kW = 1 kJ/s

Radiant Heat Flux — Energy Flux 1 Btu/hr·ft2 1 ft·lbf/hr·ft2 1 hp/ft2 1 kcal/hr·m2 1 kJ/hr·m2 1 Langley/hr 1 W/m2

Btu/hr·ft2 1 0.001285 2 544 0.369 0.088 3.687 0.3170

ft·lbf/hr·ft2 778.2 1 1.980E6 286.9 68.52 2 869 246.7

hp/ft2 3.930E-4 5.051E-7 1 1.449E-4 3.461E-5 0.001449 1.246E-4

kcal/hr·m2 2.71 0.003486 6 902 1 0.2388 10.01 0.8598

kJ/hr·m2 11.4 0.01459 28 896 4.187 1 41.87 3.600

Langley/hr W/m2 0.271 3.155 3.485E-4 0.004054 690.1 8 027 0.09993 1.163 0.02388 0.2778 1 0.08598 11.63 1

Thermal Conductivity 1 Btu/hr·ft·°F 1 Btu·in/hr·ft2·°F 1 cal/s·cm·°C 1 kcal/hr·m·°C 1 W/m·°C

Btu/hr·ft·°F 1 0.08333 24 181 0.6720 0.5778

Btu·in/hr·ft2·°F 12.00 1 290 291 8.064 6.933

cal/s·cm·°C 4.134E-5 3.445E-6 1 2.778E-5 2.388E-5

kcal/hr·m·°C 1.488 0.1240 36 000 1 0.8598

W/m·°C 1.731 0.1442 41 868 1.163 1


Appendix A-6

Unit Conversion Heat Transfer Coefficient 1 Btu/ft2·hr·°F 1 cal/cm2·s·°C 1 W/m2·°C

Btu/ft2·hr·°F 1 7 373 0.1761

cal/cm2·s·°C 1.356E-4 1 2.388E-5

W/m2·°C 5.678 41 868 1

Specific Heat — Specific Gas Constant 1 Btu/lbm·°F 1 cal/g·°C 1 ft·lbf/lbm·°R 1 kJ/kg·°C

Btu/lbm·°F 1 1.000 0.001276 0.2388

cal/g·°C 1.000 1 0.001276 0.2388

ft·lbf/lbm·°R 783.6 783.6 1 0.01872

kJ/kg·°C 4.187 4.187 0.005343 1


Appendix A-7

Unit Conversion: NOx ppm to lb/MMBtu† Natural Gas

Fuel Oil

1.5 1000 900 800 700 600 500 400 300

1 0.9 0.8 0.7 0.6 0.5 0.4

1.5 1000 900 800 700 600 500 400

1 0.9 0.8 0.7 0.6 0.5

300

0.4

0.3 200 150

150

0.15 100 90 80 70 60 50 40 30

0.1 0.09 0.08 0.07 0.06 0.05 0.04

15

4 3

40 30

0.04

0.01 0.009 0.008 0.007 0.006 0.005 0.004

2

15

40 30

0.02

15

0.015 10 9 8 7 6 5 4

0.01 0.009 0.008 0.007 0.006 0.005

3

0.004

10 9 8 7 6 5 4 3

0.003 1.5

0.0015 1

100 90 80 70 60 50

20

2

2 0.002

150

0.03

0.003

1.5

0.2

0.1 0.09 0.08 0.07 0.06 0.05

0.015 10 9 8 7 6 5

300 200

20 0.02

400

0.15 100 90 80 70 60 50

0.03 20

1000 900 800 700 600 500

0.3 200

0.2

Coal

0.002

1.5

0.0015 1

0.001

† ppm corrected to 3% dry O at 68 °F, 1 atm 2

1 0.001

1.5 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.15 0.1 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.015 0.01 0.009 0.008 0.007 0.006 0.005 0.004 0.003 0.002 0.0015 0.001


Appendix B-1

Gas Data

Water ——————— 62.35 1000 Specific weight, Specific heat, Btu/lb; cal/g·°C 1.0 1.0 2 Thermal conductivity, Btu·ft/hr·ft ·°F; Watt/m·°K 0.344 0.595 Absolute viscosity, lbm/ft·hr; kg/m·hr 2.72 4.05 0.0436 1.126 Kinematic viscosity, ft2/hr; 106·m2/sec lb/ft3;

kg/m3

Air (moist) ——————— 0.0763 1.225 0.240 0.240 0.0148 0.0256 0.0434 0.0646 0.567 14.68

Natural Gas ——————— 0.046 0.738 0.55 0.55 0.02 0.03 0.0266 0.0396 0.578 14.93

Gross heat release with 1 ft3 air + stoichiometric amount of natural gas or oil = about 100 Btu Gross heat release with 1 m3 air + stoichiometric amount of natural gas or oil = about 900 kcal Stefan-Boltzmann constant = 0.1713 x 10-8 Btu/ft2·hr·°R4 = 4.88 x 10-8 kcal/m2·hr·°K4 Universal gas constant, (MR) in pv=(MR)T/M, M=mole weight:

(MR) = 1,544 ft·lbm/°R·lb-mole (MR) = 84.7 m·kg/°K·kg-mole (MR) = 8.314 Joule/°K·g-mole

Velocity of sound in air at 68 °F (20 °C) and 1 atm = 1,129 ft/sec = 769.5 mph = 344.1 m/sec Volume of 1 lb-mole of any gas at 60 °F (15.6 °C) and 1 atm = 379 ft3 Volume of 1 kg-mole of any gas at 60 °F (15.6 °C) and 1 atm = 23.7 m3


Appendix C

Material Specifications


Periodic Chart of the Elements

Appendix D


Appendix E

Pipe Specifications


Nomograms for Flare Tip Sizing

Appendix F


Flare Radiation Calculations

Appendix G


Fluidic Flare Tip Cost Estimate

Appendix H


Appendix I

Hazardous Electrical Classifications, Groupings, Divisions† Class I.

Locations in which flammable gases or vapors are, or may be, present in the air in quantities sufficient to produce explosive or ignitable mixtures. Division 1 locations a. Hazardous concentrations exist continuously, intermittently, or periodically under normal operating conditions. b. Hazardous concentration may exist frequently because of repair or maintenance operations or because of leakage. c. Where breakage or faulty operation of equipment or processes which might release hazardous concentrations of flammable gases or vapors might also cause simultaneous failure of electrical equipment. Division 2 locations a. Where hazardous volatile liquids, vapors, or gases are normally confined within closed containers or closed systems from which they can escape only in case of accidental rupture or breakdown of such containers or systems, or in case of abnormal operation of equipment. b. Hazardous concentrations are normally prevented by positive mechanical ventilation but might become hazardous through failure or abnormal operation of the ventilating system. c. Areas adjacent to Division 1 locations to which hazardous concentrations of gases or vapors might occasionally be communicated. Group A: Atmospheres containing acetylene. Group B: Atmospheres containing hydrogen or gases or vapors of equivalent hazard such as a manufactured gas. Group C: Atmospheres containing ethyl ether vapors, ethylene, or cyclopropane. Group D: Atmospheres containing gasoline, hexane, naphtha, benzine, butane, propane, alcohol, acetone, benzol, lacquer solvent vapors, or natural gas.

Class II. Locations which are hazardous because of the presence of combustible dust. Division 1 locations a. Areas in which combustible dust is or may be in suspension in the air continuously, intermittently, or periodically under normal operating conditions, in quantities sufficient to produce explosive or ignitable mixtures. b. Where mechanical failure or abnormal operation of machinery or equipment might cause a combustible dust mixture to be produced, and might also provide a source of ignition through simultaneous failure of electrical equipment, operation of protective devices, or from other causes. c. Areas where dusts of an electrically conducting nature may be present. Division 2 locations a. Areas where dangerous concentration of suspended dust are not likely, but where dust accumulations might form on, or in the vicinity of, electrical equipment in sufficient quantities to produce explosive or ignitable mixtures except under conditions: 1. Where deposits or accumulation of dust may interfere with the safe dissipation of heat from electrical equipment or apparatus. 2. Where deposits or accumulation of dust on, in, or in the vicinity of electrical equipment might be ignited by arcs, sparks, or burning material from such equipment. Group E: Atmospheres containing metal dust (magnesium, aluminum, bronze powder, etc.). Group F: Atmospheres containing carbon black, coal, and coke dust. Group G: Atmospheres containing grain dust (flour, starch, pulverized sugar and cocoa, dairy powders, dried fat, etc.). Class III. Locations where easily ignitable fibers or flyings are present but not likely to be in suspension in quantities sufficient to produce ignitable mixtures. Division 1 locations a. Areas where easily ignitable fibers or materials producing combustible flyings are handled, manufactured, or used. 1. Such locations include some parts of rayon, cotton, combustible-fiber manufacturing and processing plants; cotton gins and cottonseed mills; flax processing plants; clothing manufacturing plants; woodworking shops; and establishments and industries involving similar hazardous processes or conditions. Division 2 locations a. Areas where easily ignitable fibers are stored or handled (except in the process of manufacture). 1. Such fibers include rayon, cotton (cotton linters and waste), hemp, kapok, excelsior, sisal or henequen, istle, jute, tow, cocoa fiber, oakum, baled waste, Spanish moss, and other materials of similar nature. †

Essential information defining limitations as given in NEC Article 500 Note: Some plant areas in the manufacture, handling, and storage of explosives or ammunition and nitrocellulose products such as celluloid photographic films, etc., involve conditions that are not covered by NEC classifications. This is particularly true where black powders, smokeless powder, dust from TNT, and other explosives are present. These areas require special equipment and installation methods.


40 CFR 60.18

Appendix J

a. Introduction. This section contains requirements for control devices used to comply with applicable subparts of parts 60 and 61. The requirements are placed here for istrative convenience and only apply to facilities covered by subparts referring to this section. b. Flares. Paragraphs (c) through (f) apply to flares. (c) (1) Flares shall be designed for and operated with no visible emissions as determined by the methods specified in paragraph (f), except for periods not to exceed a total of 5 minutes during any 2 consecutive hours. (2) Flares shall be operated with a flame present at all times, as determined by the methods specified with paragraph (f). (3) Flares shall be used only with the net heating value of the gas being combusted being 11.2 MJ/scm (300 Btu/scf) or greater if the flare is steam-assisted or air-assisted; or with the net heating value of the gas being combusted being 7.45 MJ/scm (200 Btu/scf) or greater if the flare is non-assisted. The net heating value of the gas being combusted shall be determined by the methods specified in paragraph (f). (4) (i) Steam-assisted and non-assisted flares shall be designed for and operated with an exit velocity, as determined by the methods specified in paragraph (f)(4), less than 18.3 m/sec (60 ft/sec), except as provided in paragraphs (b)(4) (ii) and (iii). (ii) Steam-assisted and non-assisted flares designed for and operated with an exit velocity, as determined by the methods specified in paragraph (f)(4), equal to or greater than 18.3 m/sec (60 ft/sec) but less than 122 m/sec (400 ft/sec) are allowed if the net heating value of the gas being combusted is greater than 37.3 MJ/scm (1,000 Btu/scf). (iii) Steam-assisted and non-assisted flares designed for and operated with an exit velocity, as determined by the methods specified in paragraph (f)(4), less than the velocity, Vmax, as determined by the methods specified in paragraph (f)(5), and less than 122 m/sec (400 ft/sec) are allowed. (5) Air-assisted flares shall be designed and operated with an exit velocity less than the velocity, Vmax, as determined by the method specified in paragraph (f)(6). (6) Flares used to comply with this section shall be steam-assisted, air-assisted, or non-assisted. (d) Owners or operators of flares used to comply with the provisions of this subpart shall monitor these control devices to ensure that they are operated and maintained in conformance with their designs. Applicable subparts will provide provisions stating how owners or operators of flares shall monitor these control devices. (e) Flares used to comply with provisions of this subpart shall be operated at all times when emissions may be vented to them. (f) (1) Reference Method 22 shall be used to determine the compliance of flares with the visible emission provisions of this subpart. The observation period is 2 hours and shall be used according to Method 22. (2) The presence of a flare pilot flame shall be monitored using a thermocouple or any other equivalent device to detect the presence of a flame. (3) The net heating value of the gas being combusted in a flare shall be calculated using the following equation: n HT = K • Σ CiHi i=1

where: HT=Net heating value of the sample, MJ/scm; where the net enthalpy per mole of off-gas is based on combustion at 25 °C and 760 mm Hg, but the standard temperature for determining the volume corresponding to one mole is 20 °C; K=Constant, 1.740 x 10-7 (1/ppm)(g mole/scm)(MJ/kcal) where the standard temperature for (g/mole scm) is 20 °C; Ci=Concentration of sample component "i" in ppm on a wet basis, as measured for organics by Reference Method 18 and measured for hydrogen and carbon monoxide by ASTM D1946-77 (Incorporated by reference as specified in Subpart 60.17); and Hi=Net heat of combustion of sample component "i" in kcal/g-mole at 25 °C and 760 mm Hg. The heats of combustion may be determined using ASTM D2382-76 (incorporated by reference as specified in Subpart 60.17) if published values are not available or cannot be calculated. (4) The actual exit velocity of a flare shall be determined by dividing the volumetric flow rate (in units of standard temperature and pressure), as determined by Reference Methods 2, 2A, 2C, or 2D as appropriate; by the unobstructed (free) cross-sectional area of the flare tip. (5) The maximum permitted velocity, Vmax, for flares complying with paragraph (c)(4)(iii) shall be determined by the following equation: Log10(Vmax)=(HT+28.8)/31.7, where Vmax=Maximum permitted velocity (m/sec) and HT=The net heating value as determined in paragraph (f)(3). (6) The maximum permitted velocity, Vmax, for air-assisted flares shall be determined by the following equation: Vmax=8.706+0.7084(HT), where Vmax=Maximum permitted velocity (m/sec) and HT=The net heating value as determined in paragraph (f)(3). [January 21, 1986]


Appendix K

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